TL 213 


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FL 213 
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Copyright 1919, by Cedric S. Webster. 


ihH 1919 


©CU5'32567 

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Contents 


Page 

Preface....:. 5 

Elementary Electricity . 7 

Magnetism .. 7 

Law of Magnetism. 8 

Law of Induction. 8 

Electricity Cannot be Stored . 9 

The Difference Between a Permanent and Electro JMagnet. 9 

The Direct Current Generator is not Adapted to Ignition 

Purposes . 10 

The Low Tension Magneto. 10 

The Difference Between a High and Low Tension Magneto.10 

Magneto Consists of .10 

Like Poles of Magnets Repel and Unlike Poles Attract.12 

Armatures ..:.14 

Primary Winding... 15 

Interrupter Points ..:.16 

Condenser . 17 

Secondary Distributor...-. 18 

Rule for Advancing and Retarding Spark... 18 

Rules for Timing Magneto Within Itself.18 

High Tension Induction Coil.19 

Magnet Charging . 21 

Rule for Making a Magnet Charger.1...22 

High Tension Magneto. 23 

Condenser Testing . 28 

Coil Testing. 29 

Instructions for Bosch High Tension D. U. Types.31 

Generation of Current.31 

Primary or Low Tension Circuit...32 

Secondary or High Tension Circuit.33 

Safety Spark Gap. 34 

Timing Range.35 

Cutting Out the Ignition .36 

Care and Maintenance.:. SI 



























































Page 

Trouble, Cause, and Remedy .37 

Other Faults . 39 

Summary of Troubles . 41 

Spark Plugs .:....42 

Installation of Magneto . 43 

Timing the Magneto . 43 

High Tension Cable Connection.44 

Bosch Duplex Ignition System . 45 

Operation on the Battery Side..-.46 

Operation on the Magneto Side. 46 

Bosch Duplex Coil ...,...48 

Switch. 49 

Battery .^.^.49 

Starting the Engine.50 

Current Consumption .51 

Connections ..51 

Battery System Must not be Grounded. 52 

Installing the Duplex System .53 

Care and Maintenance.54 

The ‘'G4-II Edition'' Magneto.57 

Installation .58 

Maintenance . 60 

Locating Troubles and Remedying Them.61 

Eisem^nn High Tension Dual System. 63 

Installation . „.66 

Maintenance .:. 69 

Locating Troubles and Remedying Them.70 

Principle of the Dixie Magneto .72 

Relation of Magneto Speed to Engine Speed.72 

Speed Table.73 

Range of Spark Advance...73 

Safety Spark Gap. 74 

The Dixie Unidirectional Magneto. 74 

Oiling .75 

Instructions for Installing . 75 

Setting the Distributor. 76 

The Late Type Battery Ignition System. 77 

Questions and Answers.,.81 























































PREFACE 


This book has been written in simple and concise language, 
especially for the beginner, or any one who desires to get a better 
understanding of the magneto, and the ignition system of the 
automobile. T have left out all unnecessary theory, and have only 
used that which is practical. 

Although the low tension magneto has gone out of date, it 
will be well to know something of its operation. In fact, the low 
tension magneto system, when being operated with the switch on 
the battery, works exactly the same as do all the late battery 
systems. So if you get the fundamental principles of this system, 
you will know them all. 

After this subject will come the high tension magneto, which 
is used on most all of the airplane, truck, and tractor motors. It is 
also used on many of the high priced cars. 

In the latter part of this book, there are special instructions 
on the Bosch and Eisemann magnetos, which I am using by 
courtesy of the Bosch and Eisemann people. 


Cedric S. Webster. 


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ELEMENTARY ELECTRICITY 


No one knows just what electricity is, any more than that it 
is a form of energy which exists in everything. The earth is a 
vast reservoir of it, and we can neither manufacture nor destroy 
it. But we can set it in motion and make use of it by an electrical 
generator or dynamo. 

Electricity, like water or air, will not move or flow without 
some kind of force or pressure to put it in motion. 

Water can be set in motion by working a pump with any kind 
of power. Air can be set in motion by the use of a tire pump. You 
can hold your finger over the end of the tire pump, and can feel 
no pressure, but by working the handle up and down you can feel 
a pressure. 

Now, electricity is set in motion by a magnetic force. Mag¬ 
netism is always present where there is a current of electricity. 
And you all know that magnetism will attract certain kinds of 
metal. 


MAGNETISM 

Magnetism is a phenomenon of which we know very little, 
and cannot be insulated, it will go through any kind of material, 
even glass or rubber. However, we can control it by the use of a 
few simple rules. And it is so closely related to electricity that 
it might well be called electricity in another form. 

If magnetism should cease to exist, for a few seconds, our 
electrical generators would be of no further use, as it is magnetism 
that sets the electricity in motion. With a magneto we have the 
permanent magnets to furnish our magnetic field. The later gen¬ 
erators, such as are used on the cars of to-day, for charging the 
battery, etc., are of the electro-magnet type; but there is always 
enough magnetism retained in the field cores to start the genera¬ 
tor going. This is called residual magnetism. 


8 


MAGNETOS AND IGNITION PRINCIPLES 


LAW OF MAGNETISM 

Take a piece of soft iron or steel and wind an insulated 
wire around it, then send a current of electricity through the wire, 
and the core will become magnetized. One end will be a north pole, 
and the other a south pole. The lines of magnetic force will flow 
from north to south pole through the air. These lines of force are 
called the magnetic field. This kind of a magnet is called an 
electro-magnet, and will only be a magnet during the time a cur¬ 
rent of electricity is passed through the wire. 

In winding an electro-magnet it is very important that you 
wind the wire in one direction, regardless of the number of layers. 
It may be wound either right or left hand, so long as ah thf» 
layers of wire run in one direction. 

If you hold an iron bar or core in your left hand, and wind an 
insulated wire around the core, in a left hand direction, then send 
a current through the wire in the same direction, the end you 
started on will be a south pole and the other end will be a north 
pole. Should you send a current through the wire in an opposite 
direction, the polarity of the magnet would be reversed. In 
other words, the north and south poles would change ends. You 
can also find the polarity with a compass. The end of the needle 
that points to the north pole of the earth, will point to the north 
pole of the magnet. 

The strength of an electro-magnet is governed by the number 
of turns of wire, the strength of the current flowing, and the 
quality of the path through which the lines of force have to flow. 

LAW OF INDUCTION 

When a coil of wire is placed in a magnetic field and the 
strength of the field is varied, it will induce a current in the wire. 
Or if the magnetic field remains steady and the coil of wire is 
revolved, or moved rapidly in the magnetic field, it will induce a 
current of electricity in the wire. 

This law of induction governs all coils, motors, and gen¬ 
erators. 

When an armature is revolved in a magnetic field it cuts the 
lines of force, which causes a current to flow in the arniiature 



MAGNETOS AND IGNITION PRINCIPLES 


9 


winding, or winds as the case may be. Miost of the authorities 
agree that the electricity is always in the wire, the same as air 
is always in a hollow tube, and the generator merely sets the 
electricity in motion, by cutting the magnetic lines of force. 

ELECTRICITY CANNOT BE STORED 

We do not store the electricity even in the storage battery, 
we store the electromotive force instead, which is called the E. M. 
F. If you put an ampemetei* on each side of the storage battery, 
while it is being charged, you will find that there will be as much 
current come out of the negative side, as there is goes in the 
positive side. And when we use current, from the battery, to 
operate the starting motor, the current all returns back to the 
battery, so you can see that it is not consumed or used up by the 
starting motor. But it does lose its E. M. F. It is the E. M. F. 
that is stored and not the electricity. A battery that is said to be 
discharged, has just as much electricity as one that is fully 
charged. But before the electricity will flow it must be charged 
with an electromotive force. Let us liken the battery to a room 
with all the doors and windows closed: of course there is air in 
the room, but there must be a pressure before it will move, or be¬ 
fore you will be aware of its presence. By opening a couple of 
doors or windows, when there is a breeze, you can feel its pressure. 

All generators produce an alternating current, but the so 
called direct current generator, by the use of a commutator trans¬ 
forms the alternating into a direct current before it leaves the 
generator. 

THE DIFFERENCE BETWEEN A PERMANENT AND 
ELECTROMAGNET 

A permanent magnet is made of hard steel and retains its 
magnetism. An electro-magnet is made of soft iron, over which is 
wound an insulated wire, and when a current of electricity is 
passed through the wire, the core becomes magnetized, with a 
magnetic field surrounding the core. The instant the current stops 
flowing, the core will cease to be a magnet, and the core is said to 
demagnetize or die out. All magnetos, direct current generators. 



10 


MAGNETOS AND IGNITION PRINCIPLES 


low voltage cut outs, and induction coils, work on the principle of 
an electro-magnet. 

THE DIRECT CURRENT GENERATOR IS NOT ADAPTED TO 
IGNITION PURPOSES- 

The D. C. generator will not produce a high enough voltage 
at low speed. But an A. C. generator, such as a magneto, will 
produce a high voltage at low speed, on account of the reversal of 
polarity every 180°, which causes a very rapid building up, 
and dying out of the armature core. This subject will be treated 
in a later chapter. 

The high tension magneto is without a doubt the most 
efficient and reliable ignition on earth. For this reason it is used 
on most all of the aeroplane, truck, and tractor motors. It is 
also used on a great many of the high priced cars, such as the 
Pierce-Arrow, Locomobile, White, and many others. 

THE LOW TENSION MAGNETO 

The low tension magneto has one primary winding on the 
armature, and only puts out from 6 to 30 volts, therefore it must 
have a high tension induction coil in connection with it in order 
to ‘'step up'' the voltage, and make it sufficiently strong to jump 
the air gap at the spark plugs. This requires a voltage of 10,000 
or more. It sometimes reaches near 30,000 volts. Taking all 
coils in consideration, the voltage would be anywhere from 12,000 
to 25,000. 

THE DIFFERENCE BETWEEN A HIGH AND LOW 
TENSION MAGNETO 

A high tension magneto has two windings, therefore does not 
need a coil. It is complete within itself. This subject will be 
treated later. 

MAGNETO CONSISTS OF 

A magneto consists principally of, a set of permanent mag¬ 
nets, two soft iron pole shoes, a non-magnetic base, armature, cam, 
breaker box, and distributor. 




MAGNETOS AND IGNITION PRINCIPLES 



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12 


MAGNETOS AND IGNITION PRINCIPLES 


The magnets are called permanent magnets because they are 
made of hard steel and once they are magnetized they retain their 
magnetism almost indefinitely. Heat and vibration are the 
chief causes of magnets losing their strength. Were it not for the 
heat and vibration of the motor, the magnets would probably hold 
their strength for a good many years. All magnets have a north 
and south pole, and the lines of force always flow from north to 
south through the outside source, and from south to north through 
the magnets. These lines of force are called the magnetic field. 
See figure 1. Magnets are made in bar and horseshoe shapes. 
Where one magnet is placed over the other, it is called a compound 
magnet, but the single magnets, such as are used on the later high 
tension magnetos, are called simple magnets. 

LIKE POLES OF MAGNETS REPEL AND UNLIKE 
POLES ATTRACT 

When magnets are placed over the pole shoes, when assem¬ 
bling, be sure and have all north poles on one side and all south 
poles on the other: it makes no difference which side they are 
placed on, so long as all like poles are on the same side. It is not 
necessary for you to know which are the north or south poles; just 
put them together so they have no attraction for each other. The 
strength of a magnet can be tested with a magnetmeter, or by 
placing an iron bar across the two ends of the magnet, then take a 
small spring scale and put the hook in the center of the iron bar and 
pull steadily. Magnets should pull from 15 to 28 pounds, depending 
on the size of the magnet and the quality of the steel. See figure 5. 

The function of the magnets is to create a magnetic field, in 
which the armature revolves. A soft iron bar called a ''keeper’’ 
should be placed across the magnets as soon as they are removed 
from the magneto, to keep them from losing their strength. 

A magneto will not give a good spark, no matter how well it 
is adjusted, if the magnets are weak. Magnets should always be 
recharged, when for any reason the magneto has been removed 
from the motor, where you have a charger at hand. 

The pole shoes, or pole pieces are made of soft iron. They are 
placed inside of the magnets and form a semi-circle to fit the shape 




DIRECTION OF FLOW OF fv\F\&NE.TIC LINES OF FORCE. 


MAGNETOS AND IGNITION PRINCIPLES IS 


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14 


MAGNETOS AND IGNITION PRINCIPLES 


of the armature. The armature revolves between the pole shoes 
and has a clearance of a few thousandths of an inch. 

The base or bottom of a magneto is made of a non-magnetic 
material—usually aluminum or brass is used for this purpose. 
While these non-magnetic materials will not insulate magnetism, 
they do offer a high resistance; and as air offers 280 times 
resistance that the core of the armature does, it is evident that all 
the lines of force will go through the armature. Now as the 
armature revolves it will cut all the lines of force. This is how the 
magneto gets its pressure or voltage, to set the electricity in mo¬ 
tion. If the base of the magneto were made of iron or steel, some 
of the lines of force would go through the base and its efficiency 
would be decreased considerably. 

ARMATURES 

There are three types of armature used on magnetos—shuttle, 
inductor, and rotor. The shuttle is the standard type and has the 
winding on the annature. All armatures are made of soft iron; 
that is the core is soft iron, the ends are made of a non- magnetic 
material. The core of all alternating current generators should 
be laminated. A laminated core is composed of sheets of soft iron, 
and insulated with a special varnish, and pressed tightly together. 
This is for the purpose of reducing eddy currents to a minimum, 
and giving a greater surface to flow of the magnetic flex. Eddy 
currents are induced electrical occurring when a solid metallic 
body is revolved in a magnetic held. Eddy currents consume a 
large amount of energy and often cause a harmful rise in tempera¬ 
ture. 

On this type of armature the lines of force reverse in direction 
through the armature every 180°, which would be each half 
revolution of the armature. We will mark the armature in order 
that you may'understand this action more clearly. Mark one side 
A and the other side B. The lines of force flow from north to 
south through the armature going in at A and out at B. The last 
half revolution of the armature the side marked B would be where 
A was in the first half revolution. Then the lines of force would 
go in at B and out at A. This gives a reversal of the lines of 
force, each half turn of the armature, and the current generated 





MAGNETOS AND IGNITION PRINCIPLES 


15 


in the armature winding will be alternating. See figure 2. Figure 
4 shows the primary E. M, F. and how it raises from zero to 
maximum every 180°. You will also note that each half turn of 
the armature produces a current in an opposite direction. 



Figure 4 


PRIMARY WINDING 

The primary winding consists of a few turns of comparatively 
coarse insulated wire: one end is fastened to the core, which is 
called grounding it. The other end is called the live or insulated 
end. This type of armature gives two impulses in one revolution, 
one every 180°. See figure 4. 

The inductor type armature is not used as extensively as the 
shuttle type, but is used on either high or low tension magnetos. 
On this type of armature the winding remains stationary and the 
inductors revolve. The winding surrounds the shaft between the 
inductors. The Remy inductor type gives two impulses to each 
revolution, the same as the shuttle type. While the high tension 
K W inductor type, is so arranged that it will give four current 
impulses to each revolution, by using a four-cornered cam. 

The Dixie rotor type is a high tension magneto and will be 
treated later. 
































16 


MAGNETOS AND IGNITION PRINCIPLES 


INTERRUPTER POINTS 

The interrupter points are for the purpose of making and 
breaking the primary circuit. They are also called contact points 
or breaker points. They are usually made of platinum or tungsten. 
Platinum gives better results on a magneto than any other kind of 
material. The points are opened by a cam which is keyed to the 
armature shaft, and are closed by a spring. The spark occurs at 
the spark plugs the instant the points open. It would be impos¬ 
sible to get a spark if the points did not open, as the magnetic field 
would not vary. Therefore one should see to it that the points 
open and close properly, and that they open the proper distance, 
which is about one thirty-second of an inch, or from twenty-five 
to thirty thousandths. It is always better to adjust the points 
the distance recommended by the manufacturer of the particular 
magneto, as they have made many tests in order to arrive at their 
conclusion. It is sometimes possible to improve on their adjust¬ 
ments, but not as a rule. The adjustment can be made by using 
a magneto wrench of the proper size. First loosen the lock nut, 
then points can be turned one way or another to get proper adjust¬ 
ment. The points often become pitted and should be trued up with 
platinum file, or sand paper. It is very important that they should 
seat well. In other words, they should be made to touch the 
entire surface of the points, if possible. So great care should be 
taken in this adjustment. 

Oil or grease should be kept away from the points, as either 
one will cause them to pit and burn badly, and would very likely 
cause the motor to miss, and it might stop entirely. Should such 
a thing happen, wash the points with gasoline. Where the points 
spark unusually bad when they are in proper adjustment, it would 
indicate that the condenser was not working properly, or that some 
of the connections were lose or broken. A sparking at the points, 
which is caused by poor condenser action, is a very bright and 
voluminous spark. When it is found necessary to replace the old 
condenser with a new one, you should use a condenser designed for 
the particular system, as all systems do not use the same sized 
comienser. 



MAGNETOS AND IGNITION PRINCIPLES 


17 


CONDENSER 

A condenser is placed in the primary circuit and is connected 
to the two ends of the primary; it is also connected across the 
breaker points. In other words, it is shunted across the points. 
Its functions are to keep the breaker points from excessive spark¬ 
ing and to intensify the high tension spark. It is the high tension 
spark that goes to the spark plugs; and any system where the 
spark has to jump an air gap at the plugs, is called a jump spark 
system. Now all jump spark systems have a condenser.' It may be 
I>laced anywhere in the electrical system, so long as it is con¬ 
nected across the breaker points, but the closer it is to both the 
points and the coil the better it will perform its work. It is the 
self-induced current caused by the dying out of the magnetic field, 
that goes into the condenser. This current is from 100 to 125 
volts, and it is this current that causes the trouble at the breaker 
points, when the condenser is not working properly. Now when 
the breaker points open, the current goes into one side of the 
condenser instead of following up the points, which would cause 
a sparking, and would burn the points, and cause trouble. Owing 
to the fact that each side of the condenser is insulated from the 
other, the current cannot get through, so it immediately dis¬ 
charges back through 'the primary wire over the core of the coil 
which causes a very rapid dying out of the magnetic field, and 
remagnetizes the core in a reversed direction. It is this rapid 
dying out, and building up, of the magnetic field, which causes the 
high voltage. Without a condenser the magnetic fields would die 
out so slowly that the voltage would be too low to produce a good 
spark. Due to the back kick of the condenser there is a shower of 
sparks produced at one spark plug every time the points open 
once, but cannot be detected with the unaided eye. 

A condenser is made of alternate layers of tinfoil and insulat¬ 
ing material, either paraffined paper or mica. And if a current 
can get through a condenser it is short circuited and is no good. 
A condenser is capable of absorbing, or holding, a certain amount 
of electrical energy for a short time. 



18 


MAGNETOS AND IGNITION PRINCIPLES 


SECONDARY DISTRIBUTOR 

A magneto, as well as all other ignition systems, has a secondary 
distributor. Its function is to distribute the high tension or high 
voltage current to the different spark plugs at the proper time. 
The most common type of distributor consists of a distributor 
gear, which carries a metal segment insulated with fiber, and a 
distributor plate or block which has carbon brushes that collect 
the secondary current and deliver it to the spark plugs. These 
carbon brushes have a small coil spring which presses them, out 
against the revolving segment. If they do not make good contact 
with the segment, it may cause the motor to miss. 

Before we take up the timing of a magneto (within itself) 
it must be understood that magnetos are not always driven in the 
same direction. Some motors drive a magneto right hand, which 
is called clockwise, while others drive it left hand, which is called 
anti-clockwise. A magneto can be timed to run either way. Of 
course they are timed correctly at the factory; but you might 
want to use it on a motor that would drive it in another direction 
from that which it was timed to run at the factory. 

THE RULE FOR ADVANCING AND RETARDING OF SPARK 

Advance is against the direction of rotation of the armature, 
and retard is with the rotation of the armature. To advance 
means to move the breaker box in the direction of rotation so 
that the points will open at an earlier period. Retard would be in 
the opposite direction, which would cause the points to open later. 

RULES FOR TIMING MAGNETO WITHIN ITSELF 

Pay no attention to marks on distributor or armature gear. 

1. Breaker box advanced. 

2. Points just starting to open. 

3. Armature leaving pole shoe about one sixty-fourth of an 
inch. 

4. Distributor segment making contact the full width of 
any one of the brushes. • This rule applies to either clockwise or 
anti-clockwise timing. To time clockwise, start from the left pole 
shoe, looking from the driven end. To time anti-clockwise start 
from the right pole shoe. 



MAGNETOS AND IGNITION PRINCIPLES 


19 


HIGH TENSION II^DUCTION COIL 

The high tension coil, such as is used on all jump spark ignition 
systems, and also the one used with the low tension magneto, is 
composed of a soft iron core which is usually laminated. The core 
is sometimes made up of a bundle of soft iron wire, which has been 
put through an annealing process of softening, then each wire is 
insulated with a special varnish, then all put together and used as 
one core. The core is insulated, over which is wound a few layers 
of coarse primary wire, then several layers of insulating cloth, and 
it is then W'ound with many thousand turns of very fine wire which 
is called the secondary. It is insulated the entire length of the 
wire. And is then insulated between each layer with paraffined 
paper. ^ 

The induction coil just described is often referred to as a 
^'step up coif' because the current that enters the coil is a ve'ry 
low voltage, and the current that comes out of it is a very high 
voltage. But the current that goes into the coil is not actually 
stepped up; because this current does not go to the secondary win d¬ 
ing. This primary or low voltage current is only for the purpose 
of creating a magnetic field in the coil, and the dying out of the 
magnetic field causes a current to flow in, the secondary winding. 
The current that leaves the battery or low tension magneto, never 
reaches the spark plugs on any system. The secondary or higli 
tension current originates in the coil, and when it leaves the coi\, 
it returns to the coil, as a current always returns to its source. 
The secondary and primaiy winding need not be connected tc- 
gether, and on some coils they are not. 

The coil just spoken of works on the dying out principle, whilcf 
some work on the building up principle. Any change in the 
strength of the magnetic field will induce a current in the wind¬ 
ing, or windings, as the case may be. 

The voltage of an induction coil depends upon the strength 
of magnetic field, the number of turns of wire, and the rapidity 
with which it builds up or dies out. The voltage of an induction 
coil is anywhere from 12,000 to 25,000. 

Figure 3 shows the internal wiring of a Remy L. E. coi\ 





20 


MAGNETOS AND IGNITION PRINCIPLES 


connected to a Remy magneto with the shuttle type armature. 
When running on the battery the current comes out of the 
terminal marked with a plus sign, which is the positive post of the 
battery, and goes across the switch through the primary wire, 
that is wound around the core of the coil, setting up a magnetic 
field in the coil and out the terminal Y, down to the insulated 
breaker point Y, and across the grounded breaker point through 
the ground, indicated by the dotted line, to the grounded terminal 
R, to the R terminal of the coil, out the R terminal at the bottom 
of the coil to the negative side of the battery, indicated by the 
minus sign, which completes the primary circuit. 

Now the instant the breaker points open, the primary current 
ceases to flow, and the magnetic field of the coil dies out, which 
causes a current to flow in the secondary winding which winding 
is indicated by the red wire in the coil. It then goes to the center 
of the distributer, and is distributed by the revolving segment, to 
the different spark plugs in their proper firing order. In this case 
the revolving segment is in contact with the wire leading to num¬ 
ber 1 spark plug, and the current will return through the ground 
of the engine, indicated by the dotted red line, and return through 
tiie primary wire R to the secondary winding in the coil, which com¬ 
pletes the secondary circuit. When running on the battery the 
magneto is not putting out any current, because the magneto 
circuit is not complete. Now when thie switch is turned on the 
magneto side, it completes the magneto circuit and interrupts the 
battery circuit. 

The current will now flow from the armature wire G, which 
is called the magneto lead, to the G terminal on the coil, across 
the switch through the primary wire over the core, and out at Y 
to the insulated breaker Y, to the grounded breaker, through the 
ground to the grounded end of the armature winding, thus com¬ 
pleting the magneto circuit. And when the breaker points open, 
the magneto circuit immediately stops flowing, which results in 
the dying out of the magnetic field and a current is said to be 
induced in the secondary winding, the same as when running on 
the battery. The current that leaves the secondary winding goes 
to the distributor and from there to some one of the spark plugs. 





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condenser in this system was placed in the magneto by the Remy People. 

















































MAGNETOS AND IGNITION PRINCIPLES 21 

and returns through the ground to the primary wire R and from 
there to the red wire in the coil, which is the secondary winding. 

Remember that the current that leaves the low tension mag¬ 
neto or battery, never goes to the spark plugs. The low tension or 
primary current is only for the purpose of magnetizing the soft 
iron core of the coil. The secondary current originates in the 
secondary winding, on all systems, whether the secondary winding 
is in the coil or magneto. The condenser on this Remy system 
just described was placed in the magneto by the Remy factory, 
but for convenience I have placed it in the coil, as it is on some 
of the other systems. It will work in either place so long as it is 
connected to the two primary wires that lead to the breaker points. 
See figure 3. 

MAGNET CHARGING 

Hold the magnet that is to be recharged at right angles to the 
charger, and at a distance of about 4 inches above the charger. 
Then turn the switch on, and lower the magnet gradually and it 
will seek its own polarity. Leave it there about 5 or 10 seconds, 
then rock it back and forth on the charger, then turn the switch 
off and on two or three times, and before you turn the switch off 
for the last time, place a soft iron bar usually called a “keeper'' 
across the poles of the magnet; turn the switch off, and the job 
is finished. There is no definite length of time to leave a magnet 
on the charger. However 15 or 20 seconds should be sufficient. 
Magnets should test anywhere from 15 to 28 pounds, depending on 
the size of the magnet, the quality and temper of the steel. This 
test can be made with a magnet meter, or with an ordinary spring 
scale, as previously stated under the heading of permanent 
magnets. 

If the magnet does not test what you think it should, repeat 
the operation and very likely it will test 15 or 20 pounds. A magnet 
will only hold a certain amount of magnetism, and when it is fully 
charged it is said to be saturated, and will hold no more. The 
magnets on the later magnetos will generally test from 18 to 28 
pounds. ' This does not include the magnets on a Ford. See 
figure 4. 




22 


MAGNETOS AND IGNITION PRINCIPLES 


RULE FOR MAKING A MAGNET CHARGER 
This type of charger is intended to be used with a six volt 
storage battery, or about six dry cells. Take two soft iron cores 
3 inches long by 1 inch in diameter, and drill a hole in both ends 
of each core; then thread the holes and fasten the two cores to a 
soft iron base with screws. Then take two pieces of soft iron, 
with a surface 1^2 inches square, and fasten them to the top of 
each core. Make these connections perfectly tight. The core 
should be insulated with one or two layers of tape, or some othei 
insulating material; also insulate so that the wire cannot come 
in contact with the metal at the top or bottom. A thin piece of fiber 
will do for his purpose. Then wind three layers of number 12 
double cotton covered magnetwire (about 37 feet) on each core. 



Figure 5 























MAGNETOS AND IGNITION PRINCIPLES 


23 


Wind the wire on the cores in an opposite direction to each other, 
thus making one a north and the other a south pole, and apply a 
coat of shellac on each winding to protect the insulation. You can 
now put on some kind of a switch. See figure 5. The arrows 
show the direction of the flow of the lines of force. 

HIGH TENSION MAGNETO 

The high tension magneto is complete within itself because it 
has two windings on the armature, and has the condenser some 
place in the magneto. We will first consider a high tension mag¬ 
neto with a shuttle type armature (which is the standard type). 
On this type of armature the condenser is placed in one end of 
the armature, and is connected in shunt with the primary winding 
and the interrupter points. Shunt means the same as parallel. 

We might say that the high tension magneto has the in¬ 
duction coil on the armature, and works on the same principle as 
does the low tension magneto system. 

A high tension magneto of this type, consists principally of a 
couple of permanent magnets, two soft iron pole shoes, a bottom 
or base made of a non-magnetic material, an armature with two 
windings, and a secondary distribution. 

The high tension magneto is an alternating current genera¬ 
tor, the same as all other magnetos, and generates a current by 
cutting lines of force. The primary winding of this type of mag¬ 
neto consists of a few layers of coarse insulated wire, one end is 
grounded to the core of the armature, and the other is the 
insulated end, which is connected to the insulated interrupter point 
by the interrupter holding screw. The other interrupter point is 
gi'ounded, which makes a connection through the ground to the 
ground end of the primary wire, which completes the primary 
circuit when the interrupt el* points are together. 

The secondary consists of about sixty or seventy layers of very 
fine insulated wire, and is insulated with paraffined paper, between 
each layer of v/ire, to keep the current from shorting. The second¬ 
ary is grounded to the primary, not because it has to be, but it is 
done for convenience. The other end of the secondary is the insu¬ 
lated end and connects to the collector ring or slipring, which is lo- 




24 


MAGNETOS AND IGNITION PRINCIPLES 



cated on one end of the armature. The slipring is insulated on each 
side with hard rubber. There is a carbon collector brush which 
collects the current from the slipring and passes it through a con¬ 
ducting rod to the center of the distributor, and from there it is 
distributed to the different spark plugs in their order. And after 
the spark jumps the air gap in the spark plug it returns through 
the ground of the engine back to the grounded end of the 
secondary. It must be remembered that the armature revolves in 
the magnetic field, which is created by the permanent magnets, 
and each 180° of the armature travel, brings a different side of the 
armature to the side, that the north pole is on. Consequently the 
lines of force are reversed through the armature every 180°, which 
generates an alternating current. See figure 2. The shuttle type 
armature gives two current impulses to each revolution of the 
armature, which will produce a spark every 180°, or each half 
turn of the armature. See figure 4. 

So one time the spark goes through the wire to the spark plug 
and returns through the ground of the engine, back to the 
secondary winding. And the next 180° the spark goes through 
the ground first, and jumps the air at the plug and returns 
back through the wire to the distributor and then to the secondary 
winding. 




















MAGNETOS AND IGNITION PRINCIPLES 


25 


This is not the case with the battery system, because it sends 
out a direct current. 

During the time the armature is passing from a horizontal to 
a vertical position the interrupter points are closed, which com¬ 
pletes the primary circuit, and there is a current being generated 
in the primary winding, which helps the permanent field magnetize 
the core of the armature, and as soon as the armature reaches a 
vertical position the lines of force from the permanent field, go 
through the two heads of the armature, and at this position the 
interrupter points open, which causes the ‘'neck’' of the armature 
to die out, and the dying out of the “neck” or core induces a cur¬ 
rent in the secondary winding. So it is very important that a mag¬ 
neto be timed so that the interrupter points will open just as the 
armature is leaving the pole shoe. 

The voltage of the primary winding of a high tension mag¬ 
neto, taking all makes into consideration, is anywhere from 30 to 
60 volts. And the secondary is from 10,000 to 20,000 volts, de¬ 
pending on the speed of the armature. The faster it is driven 
the higher the voltage. A high tension magneto has a safety gap, 
to protect the secondary winding and keep it from burning out, 
in case one of the spark plug wires should become disconnected 
between the distributor and the spark plugs, etc. The distance 
of the safety gap is usually from % to 1/2 i^^ch. 

Should the hard rubber insulation on the collector ring get 
broken or cracked, it would be necessary to put on a new collector 
ring. This can be done by taking off the ball bearing and ball 
race. And one should have a regular ball race puller for this 
piirpose. After the bail race has been taken off, you can take a 
hardwood stick and place it on the hard rubber tube, where the 
secondary wire enters the collector ring, and pound lightly. The 
secondary wire sticks in the hard rubber tube but is nt fastened 
in any way, so you should not experience much trouble in remov¬ 
ing the collector ring. In replacing the new one be very careful 
not to crack the hard rubber insulation. Line up the projecting 
tube of the collector ring, with the hole in the end of the armature 
and push it on as far as it will go with your hands, then put on the 



2« MAGNETOS AND IGNITION PRINCIPLES 


ball race, and push it on with an arber-press, or take a piece of 
hollow pipe the proper size and slip over the end or the armature, 
and place it in a vice, and screw the vice up gradually and take 
great care not to push the ball race on too far, but it must be far 
enough to allow the ball race to be in perfect alignment with the 
ball ring in the end of the magneto end plate. You should also 
take great care in starting the end of the secondary wire into the 
bole of the hard rubber tube on the collection ring, so as not to 
allow it to bend or curl up, as it might not make a good connection. 



MAGNETOS AND IGNITION PRINCIPLES- 


27 



CONDENSER ARMATURE COLrE’CTOR RINQ 

WINDIN C^ 

Figure 6 


To get at the condenser remove the ball race at the rear end^ 
of the armature in this particular case, then take the screws out 
of the end of the armature. You can then take a soldering iron 
and melt the two soldered connections of the condenser, and it can 
then be removed. In replacing the condenser be sure that it is- 
in good condition, and solder the connections tightly. Never at^ 
tempt to repair the windings of an armature, as that is a regular 
factory job, and requires a special skill and machinery. It is not 
necessary to be an armature winder in order to be a first-class 
electrician, but it is necessary to be able to test armatures, etc. 

An armature can be tested with a 110 volt D. C. or A. C. light¬ 
ing system, by using a lamp in series with the test wires. To test 
the primary, hold one of the test wires on the insulated lead, and 
the other to any part of the armature, that is a ground, and if the 
lamp lights it shows that the primary winding is not broken, and 
IS very likely all right. However, it may be short circuited. To^ 
test the secondary, place one of the test wires on the collector ring 
and the other on the ground, which will be most any place on the 
armature; the lamp will not light, but if there is no open circuit 
in the winding, you will note a small spark at your test wire hy 
making and breaking the circuit. Should the lamp light it would 
show that there was a partial short circuit. For a final test, be 
sure that everything else is in first-class condition, then assemble 
the magneto, and if you have the equipment run the magneto at a 
speed of about 45 revolutions per minute and if the spark will not 




28 


•MAGNETOS AND IGNITION PRINCIPLES 


jump a gap one sixteenth of an inch wide, it is very likely that 
two or more of the layers of the secondary winding are shorted. In 
this case it will be necessary to replace the armature. 

Another test for an armature is to use a storage battery, or 
six dry cells connected in series. Take two test wires leading 
from each side of the battery, and put one on each end of the 
primary winding. If you do not know where the two ends are, 
hold one wire on the ground, and keep trying with the other wire 
until you get a coil or primary flash. Of course if you get a coil 
flash the primary winding is all right. On the high tension mag¬ 
neto with the shuttle type armature, it will be found very con¬ 
venient to take the interrupter off, then put the fastening screw 
back in the end of the armature, which makes a connection with 
the insulated end of the primary winding. Then take a wire and 
place one end on the collector ring and the other end about Ys of 
an inch from the armature. Again take the two battery wires 
and touch them to the two ends of the primary, and make and 
break the circuit which should cause a spark to jump the Ys inch 
air gap. In fact, if everything is all right it should jump about % 
of an inch. After this test is made assemble the magneto and 
give the armature a quick turn by hand and if you can make the 
spark jump Ys of an inch, the magneto is all right. You should 
never make and break the primary circuit, without having a 
circuit for the secondar 5 % as it might puncture the secondary 
winding. 


CONDENSER TESTING 

To test a condenser, take two test wires and connect to a 110 
volt D. C. or A. C. lighting system, with a lamp in series, then 
connect the two test wires with the two condenser wires, and if 
the lamp lights the condenser is short circuited and is no good. 
See figure 7. However, if the lamp does not light, it may still be 
no good; it may be what is called opened circuited. To test for 
an open circuit, first touch your two test wires together, then make 
and break the circuit, and note the spark. Then connect one con¬ 
denser wire to each one of the test wires, and again make and 
break the circuit, and if the condenser is all right you will note a 



MAGNETOS AND IGNITION PRINCIPLES 29 

snappy spark: if you note no difference in the spark, with the 
condenser in and out of the circuit, it is no good and should be 
replaced with a new one. The new one should also be tested, to 
make sure that it is all right before it is placed in the system. 


'110 OR zro VOLT 
nx-OR V.C. 



A simple test for a condenser is to connect it to a 110 or .220 
volt circuit, direct or alternating current, with a lamp connected 
in the circuit in series with the condenser. When the condenser 
is in good condition, there should be no circuit through the con¬ 
denser when the switch is closed and the lamp should not light. If 
the lamp lights the condenser is defective and should be replaced. 

An extra good condenser will hold a charge for fifteen or 
twenty seconds, and sometimes longer. To make this test, take 
the two test wires and place on the two condenser wires, which 
will charge the condenser, then take the test wires off, and strike 
the two condenser wires together, and you should note a small 
spark. However, if this test fails, use the one in the preceding 
paragraph. On some systems one side of the condenser is 
grounded; in this case ground one of your test wires, and after 
they have been removed touch the condenser wire to the ground, 
and you should see a small spark. 

It would be well to have a condenser on hand for testing 















30 


MAGNETOS AND IGNITION PRINCIPLES 


purposes. You will find it very convenient to have wires about six 
inches or a foot long on each condenser terminal. Then when 
you see an excessive amount of sparking or flashing at the inter¬ 
rupter points, and a weak spark at the spark plugs, you can con¬ 
nect the two wires of your test condenser across the interrupter 
points. If this stops most of the sparking and strengthens the 
spark at the plugs, it will show that the condenser in the system 
is not working properly. Where one of the interrupter points is 
grounded you can ground one of the condenser wires. ‘ 

COIL TESTING 

To test a coil, you can use 110 volt D. C. or A. C. the same as 
used for condenser testing, with lamp in series. Where the switch 
is on the coil, it will be necessary to turn the switch on, but this 
will not be necessary in testing the later coils. Put the two light 
wires on the primary terminals; if the lamp lights the primary is 
very likely all right. That is, there is no open circuit. Then put 
one of the wires on the secondary or high tension terminal, and 
the other to the secondary ground, (which is either grounded to 
one of the primary wires, or to the core of the coil). The lamp 
will not light, but if secondary is all right you can see a small spark 
by making and breaking the circuit. If the lamp lights the wind¬ 
ing is short circuited. 

The primary winding can be tested by using two test wires 
connected to a six volt battery, by placing the two test wires to 
each one of the primary, terminals, and by making and breaking 
the circuit it will induce a current in the secondary winding; in 
this case put a wire on the secondary terminal, and place the other 
end of the wire about % or 1/2 inch from the secondary ground; 
then make and break the primary circuit, and if everything is in 
good order the spark will jump the air gap between the secondary 
wire and the ground. If there is no condenser in the coil, it may 
be necessary to connect a condenser to the primary wires in order 
to make the spark jump the gap. If it will jump a I /2 inch in 
the open, it will insure a good spark under compression, as it 
takes about 15,000 volts to jump a ^2 inch air gap. In making this 
test be sure and have a circuit for the secondary, otherwise it 
might damage the winding. 




MAGNETOS AND IGNITION PRINCIPLES 


31 


INSTRUCTIONS FOR BOSCH 
D U TYPES 

The Bosch Magnetos, Types 
DUl, DU2, DU4-2, DUS, DU4 
and DUG, are of the high ten¬ 
sion series, and are used respec¬ 
tively on one, two, three, four, 
and six-cylinder engines of the 
automobile type, in motor car, 
marine, tractor, and stationary 
service. 

The type DU magnetos are 
usually employed as sole ig¬ 
nition on an engine, or, in some 
cases, in connection with a bat¬ 


HIGH TENSION MAGNETOS 



Figure 8. 


tery system operating on a separate set of spark plugs. The DU 
magnetos, without alteration, are also employed to provide battery 
and magneto ignition on one set of spark plugs, this being ac¬ 
complished by means of the Bosch Vibrating Duplex Ignition Sys¬ 
tem, a separate booklet describing which may be had on request. 
The Bosch Independent Magnetos, DU Types, are those described 
in this booklet. 


GENERATION OF CURRENT 


Like other Bosch High Tension Magnetos, the types DU gen¬ 
erate their own high tension current directly in the magneto arma¬ 
ture (the rotating member of the magneto), without the aid of a 
separate step-up coil, and have their timer and distributor integral. 

The armature winding is composed of two sizes of wire, one 
size comparatively heavy and the other very fine. The heavy wire 
constitutes the primary or low tension circuit, and the very fine 
wire the secondary or high tension circuit. 

The rotation of the armature between the poles of strong 
pei-manent magnets sets up or induces a current in the armature 
primary circuit, and this is further augmented at regular intervals 
in the rotation of the armature shaft by the abrupt interruption of 
the primary circuit by means of the magneto interrupter. At the 




32 


MAGNETOS AND IGNITION PRINCIPLES 


opening of the prinxary circuit, the resulting discharge of current 
from that circuit induces a current of high voltage in the armature 
secondary circuit. The high tension current thus created is col¬ 
lected by the slipring on the armature and passed through the 
slipring brush, then to the various magneto distributor terminals, 
each of which is connected by cable to the spark plug in its re¬ 
spective cylinder. The operation of the instrument will be more 
clearly understood from a study of the complete circuits, primary 
and secondary, which follow. 



Figure 9. 

PRIMARY OR LOW TENSION CIRCUIT 
The beginning of the armature primary circuit is in metallic 
contact with the armature core, and the end of the armature pri¬ 
mary cii'cuit is connected, by means of the interrupter fastening 
screw, to the insulated contact block supporting the long platinum 
contact on the magneto interrupter. The interrupter lever, carry¬ 
ing a short platinum contact, is mounted on the interrupter disc 
which, in turn, is electrically connected to the armature core. The 
primary circuit is completed whenever the two platinum inter¬ 
rupter contacts are brought together, and interrupted whenever 
these contacts are separated. The separation of the platinum con¬ 
tacts is controlled by the action of the interrupter lever as it bears 
against the steel segments secured to the inner surface of the 






















MAGNETOS AND IGNITION PRINCIPLES 


3S 


interrupter housing; the types DUl and DU4-2, 360°, are each pro¬ 
vided with but one interrupter segment, while all other DU types 
have two such segments. 

The high tension current is generated in the secondary circuit 
only when there is an interruption of the primary circuit, the 
spark being produced at the instant the platinum interrupter con¬ 
tacts separate. 

SECONDARY OR HIGH TENSION CIRCUIT 

The armature secondary circuit is a continuation of the arma¬ 
ture primary circuit, the beginning of the secondary being con¬ 
nected to the primary, while the end of the secondary is connected 
to the insulated current collector ring, or slipring, mounted on the 
armature just inside the driving shaft end plate of the magneto. 
This form applies in all DU types except the DUl two-spark 
magneto. 

In Types DU4-2, DUS, DU4 and DUG, the slipring brush, 
which is held in contact with the slipring by the brush holder at 
the shaft end of the magneto, receives the high tension current 
collected by the slipring and, by means of the connecting bar under 
the arch of the magnets, passes the current to the metal contact 
in the center of the distributor plate. From the latter point the 
high tension current passes to the distributor brush, which is held 
in a brush holder mounted on the distributor gear and, conse¬ 
quently, rotates with the gear. 

Metal segments are imbedded in the distributor plate, and as 
the distributor brush rotates, it makes contact successively with 
the segments in the distributor plate. 

The segments in turn are connected with the terminal studs 
on the face of the distributor plate, and the latter are connected 
by cables to the spark plugs in the various cylinders. In the 
cylinders, the high tension current produces a spark which causes 
ignition and then returns through the engine to the magneto arma¬ 
ture, thus completing the circuit. 

In Type DU2, the slipring groove is provided with a sectional 
metal segment, and the end of the armature secondary circuit is 
connected to this segment. The metal segment acts not only as a 




34 


MAGNETOS AND IGNITION PRINCIPLES 


current collector, but also as a high tension distributor, for, at 
every 180*^ revolution of the armature, the segment alternately 
comes into contact with, and delivers high tension current to, one 
of the two slipring brushes which are horizontally mounted in the 
brush holders on opposite sides of the shaft end plate. High 
tension cables from the brush holder terminals connect the slipring 
brushes with the spark plugs in the cylinders. 

In Type DUl, Single-Spark, for one-cylinder engines, no 
distributor is required, and the high tension current from the 
armature secondary circuit is passed by the slipring to a single 
brush, which is supported by a brush holder at the shaft end of the 
magneto. A high tension cable between the brush holder terminal 
and the spark plug in the cylinder completes the secondary circuit. 

In Type DUl, Two-Spark, the armature secondary circuit is 
insulated from the armature primary circuit, and the two ends of 
the secondary are connected to two sectional metal segments, dia¬ 
metrically opposite on a single slipring. Two slipring brushes are 
provided which, as in the type DU2, are horizontally mounted in 
brush holders on opposite sides of the shaft end plate; during that 
portion of the armature rotation when high tension current is 
being delivered, each of the two slipring segments will be in con¬ 
tact with one of the brushes. The secondary circuit is completed 
by a high tension cable from each brush holder terminal to a 
spark plug, and a spark will pass at both plugs simultaneously. 

SAFETY SPARK GAP 

In order to protect the armature and other current carrying 
parts, a safety spark gap is provided. 

Under ordinary conditions, the current will follow its normal 
path to the spark plug, but if for any reason the electrical resist¬ 
ance in the secondary circuit is increased to a high point, as when 
a cable becomes disconnected or a spark plug gap too wide, the 
high tension current will discharge across the safety gap. 

The current should never be allowed to pass across the safety 
spark gap for any length of time, and if the engine is operated on a 
second or auxiliary ignition system, the magneto must be grounded 
in order to prevent the production of high tension current. The 



MAGNETOS AND IGNITION PRINCIPLES 


35 


snapping sound by which the passage of the current across the 
safety gap may be noted should always lead to an immediate search 
for the cause of the difficulty. 

In Types DU4-2, DUS, DU4 and DUG, the safety spark gap 
is arranged on the dust cover over the armature, and consists of 
two short pointed electrodes.supported a short distance from each 
other; one electrode is set on the dust cover itself and inclosed by a 
metal and wire gauze housing, while the other, or insulated 
electrode, is set in the center of the steatite cover of the safety 
spark gap housing and connected into the secondary circuit of the 
magneto. 

In Types DUl and DU2, the safety spark gap consists of a 
shcit pointed wire projecting from the armature insulating ma¬ 
terial, the end of this wire extending to within a short distance 
of the armature cover at the driving shaft end. 

TIMING RANGE 

The magneto interrupter hous¬ 
ing is arranged so that it may be 
rotated through an angle of 35® 
with respect to the armature 
shaft. The movement of this hous¬ 
ing in one direction or the other 
causes the interrupter lever to 
strike the steel segments earlier or 
later in the revolution of the arma¬ 
ture, the spark occurring corre¬ 
spondingly earlier or later in the 
stroke of the piston. 

The spark can be advanced by 
moving the interrupter housing, by 
means of the timing control arm, in 
the direction opposite the rotation of the armature, and can be 
retarded by moving the interrupter housing in the same direction 
as the rotation of the armature. The armature rotation is indi¬ 
cated by the arrow on the oil well cover at the driving shaft end 
of the magneto. 



P^igure lu. 

Bosch Magneto Type DU2 




36 


magnetos AND’ IGNITION PRINCIPLES 



Figure 11. 


1. Brass plate for connecting the end 
of armature primary circuit. 

2. Fastening screw for magneto in¬ 
terrupter. 

9. Condenser. 

10. Slipring. 

11. Slipring brush. 

12. Slipring brush holder. 

13. Slipring brush holder. 

14. Connecting bar. 

15. Distributor brush holder. 

16. Distributor brush. 


17. Distributor .plate. 

18. Central distributor contact. 

20. Terminal nut for distributor 
plate. 

22. Dust cover over armature. 

24. Terminal nut for grounding 
terminal. 

116b. Interrupter housing and timing 
arm. 

117. Cover for interrupter housing. 

118. Contact Spring for grounding 
terminal. 


CUTTING OUT THE IGNITION 
Since high tension current is generated only on the inter¬ 
ruption of the primary circuit, it is evident that in order to cut 
out the ignition it is necessary merely to divert the primary 
current to a path which is not affected by the action of the mag¬ 
neto interrupter. This is accomplished as follows: 

An insulated grounding terminal is provided on the cover of 
the magneto interrupter housing with its inner end, consisting of 
a spring with carbon contact, pressing against the head of the 
interrupter fastening screw. The outer end of the grounding 
teiininal is connected by low tension cable to one side of a switch, 
and the other side of the switch is grounded by connecting another 
cable between it and the engine or chassis. 


































MAGNETOS AND IGNITION PRINCIPLES 


37 


When the switch is open, the primary current follows its 
normal path across the platinum interrupter contacts and is inter¬ 
rupted at each separation of these contacts; however, when the 
switch is closed, the primary current passes from the head of the 
interrupter fastening screw to the carbon contact of the grounding 
terminal, thence through the switch to the engine and back to the 
magneto, and as the primary current remains uninterrupted when 
following this path, no ignition current is produced. 

CARE AND MAINTENANCE 

Aside from keeping the magneto clean externally, practically 
the only care required is the oiling of the bearings; of these, there 
are two ball bearings supporting the armature, and in the types 
with gear driven distributor,, a single plain bearing supporting the 
shaft of the distributor gear. 

Any good, light machine oil may be used for this purpose 
(never cylinder oil), and each of the bearings should receive not 
more than two or three drops about every 500 miles, applied 
through the oil ducts under the covers marked located at 

both ends of the magneto. 

The interrupter is intended to operate without lubrication, 
and as oil on the platinum interrupter contacts will prevent good 
contact, cause sparking and burning, as well as misfiring, care 
should be exercised to prevent the entrance of oil to these parts. 

Starting the Engine: When cranking an engine equipped with 
a DU magnet as sole ignition, the spark lever should be fully re¬ 
tarded if the magneto is of the Model 5 or Model 6 construction 
(most of the DUl and DU2 magnetos are of these models), but 
should be slightly advanced with all other models. In the latter 
case, if the magneto has been timed according to instructions, the 
spark lever may be safely advanced about one third, or even one 
half on starter equipped engines, and in this position will permit 
easier starting (see also “Plug Gap Too Wide,^’ on page 38). 

TROUBLE—CAUSE AND REMEDY 

Ignition difficulties may be divided into two main classes, one, 
the most common, due to spark plugs and cables, and the other. 



38 


MAGNETOS AND IGNITION PRINCIPLES 


comparatively infrequent, due to the magneto. In case of defective 
ignition, therefore, it must first be determined whether the fault 
is in the magneto or, as is more probable, elsewhere. 

In general, when only one cylinder misfires the fault is in the 
spark plug, the most common plug difficulties being as follows: 

Plug Gap Too Wide: The distance between the electrodes of 
the spark plugs varies according to the individuality of the engine, 
but normally this distance should not be less than l-50th inch. On 
the other hand, however, too wide a gap increases the electrical 
resistance, and interferes with the proper generation of current 
at low sped. Difficulty in starting an engine and missing at low 
speeds are very often due to the spark plug gaps being too wide 
and, as the spark will have a tendency to bum the electrodes and 
thereby gradually increase the gap, it is especially important that 
the plugs be examined occasionally for assurance that the gap is 
not too great; any difficulty due to this cause may be readily over¬ 
come by readjusting the electrodes. 

Plug Short-Circuited: This is usually caused by a cracked or 
porous insulator, or by fouling of the electrodes or insulator. Any 
of these conditions will cause misfiring by permitting the current 
to stray from its intended path. In Bosch Spark Plugs the possi¬ 
bility of trouble from such causes is reduced to a minimum. 


Longitudinal Section of DUl Magneto 

























MAGNETOS AND IGNITION PRINCIPLES 


39 


Rear View of DUl Magneto 
(Interrupter Housing Cover Removed) 

1. Brass plate for connecting the end 
of armature primary circuit. 

2. Fastening screw for magneto in¬ 
terrupter. 

3. Contact block for magneto inter¬ 
rupter. 

4. Magneto interrupter disc. 

5. Long platinum screw. 

6. Short platinum screw. 

7. Long flat spring for magneto in- 
termpter lever. 

8. Magneto interrupter lever. 

9. Condenser. 

10. Slipring. 

11. Slipring brush. 

13. Siipring brush holder. 

15. Steel segment for interrupter 

housing. 

17. Dust cover over armature. 

19. Terminal nut for grounding term¬ 
inal. 

79. Interrupter housing and timing 
control arm. 

82. Cover for interrupter housing. 

83. Spring for holding interrupter 
housing cover. 

OTHER FAULTS 

Cables: Misfiring of one cylinder, either continuous or inter¬ 
mittent, may be due also to a chafed or broken cable or to a loose 
connection. The cables should be carefully examined, special at¬ 
tention being paid to the insulation. The metal terminals of the 
cables must not come into contact with any metal parts of the 
engine or of the magneto, except those designated as being correct 
according to the instructions given. 

Ignition Fails Suddenly: A sudden failure of ignition may 
indicate a short circuit in the low tension cable, due either to a 
defect in the cable, to a faulty connection at the switch, or to the 
presence of dirt or moisture. A test for trouble in the switch or 
low tension cable can be made by removing the cable from the 
grounding terminal on the cover of the magneto interrupter hous¬ 
ing and endeavoring to start the engine on the magneto. If the 
engine runs with this wire disconnected but stops when the wire is 















40 


MAGNETOS AND IGNITION PRINCIPLES 


connected, it is evident the magneto is in good order and that the 
trouble is due to some fault in the switch or grounding wire per¬ 
mitting the low tension current to escape to ground. 

Irregular Firing: If the cables and plugs are in good con¬ 
dition, and yet the ignition is irregular, the trouble is probably 
with the magneto, and the interrupter should be carefully 
examined. It should be seen that the interrupter lever moves 
freely on its pivot, that the hexagon headed fastening screw in 
the center of the interrupter is properly tightened, and also that 
the two platinum interrupter contacts are properly secured in 
position. 

If the interrupter lever does not move freely on its pivot, which 
is sometimes possible, particularly with new magnetos, the hole in 
the fibre bushing in which the lever pivots may be slightly en¬ 
larged by means of a reamer or small round file; this work, how¬ 
ever, should be carefully done as very little reaming accomplishes 
the desired result. 

Platinum Interrupter Contacts: The platinum interrupter 
contacts should be examined for the correctness of their adjust¬ 
ment, and they should be so set that they are separated by a 
distance of 0.4 of a millimeter (about l-64th inch) when the 
interrupter lever is resting on either of the segments in the inter¬ 
rupter housing. The strip of steel attached to the Bosch magneto 
adjusting wrench, which is furnished with each magneto, is to be 
used as a gauge for this distance. The adjustment of the platinum 
interrupter contacts may be made by loosening the lock nut of the 
long contact screw, which passes through the interrupter contact 
block, and turning the hexagon head of the screw itself by means 
of the before mentioned Bosch adjusting wrench. When the 
adjustment is made, care should be taken to tighten the lock nut 
firmly. 

The platinum contacts of the interrupter should be clean and 
in proper alignment with each other, and any oil, grease or dirt 
that is deposited on them should be removed. If they are uneven 
or in bad condition (but only then) they may be smoothed by 
means of a fine, flat, jeweler’s file. The platinum contacts should 



MAGNETOS AND IGNITION PRINCIPLES 


41 


be kept clean, and in that condition and with proper attention they 
will last a considerable length of time. 

The interrupter itself may be taken out as a unit by removing 
the interrupter housing and withdrawing the hexagon headed 
fastening screw in the center of the interrupter by means of the 
Bosch adjusting wrench. Should the interrupter stick on its seat 
after the fastening screw is withdrawn, it may be pried loose by 
means of two small screw drivers inserted back of the interrupter 
disc, one on each side. When replacing the interrupter, care must 
be taken that the key on the interrupter disc fits exactly into the 
keyway on the armature shaft. 

Damaged Insulating Parts: As it sometimes happens that 
brush holders and other insulating parts of the magneto -are 
damaged through accident or carelessness, these parts should also 
be carefully examined for possible disarrangement or damage of 
the insulation which might permit leakage of current. 

SUMMARY OF TROUBLES 

In brief, providing the magneto is properly timed to the 
engine, trouble due to ignition may be as follows: 

Engine Will Not Start: Switch closed, switch or switch wire 
short-circuited, interrupter lever sticks; also, with single and two- 
cylinder types, defective or dirty spark plug, broken or discon¬ 
nected high tension cable, defective cable insulation, damaged 
brush holder. 

Engine Stops Abruptly: Switch closed, switch or switch wire 
short-circuited; also, with single and two-cylinder types, spark 
plug cable disconnected. 

Misfiring at Low Speed: Spark plug gap too wide. 

Misfiring at All Speeds: Defective or dirty spark plug, im¬ 
proper spark plug gap, cable insulation chafed, cable connections 
loose, brush holder cracked, platinum interrupter contacts dirty 
or oily, interrupter lever sticks. 





42 


MAGNETOS AND IGNITION PRINCIPLES 


SPARK PLUGS 

It may be pointed out that inasmuch as ignition defects are 
due largely to dirty or defective spark plugs, most such trouble 
can be avoided by using plugs which are properly designed and 
constructed. 

The characteristics of a suitable plug are: An unbreakable 
and positive insulator, solid construction, which absolutely pre¬ 
vents leakage, multipoint electrodes of such metal as will resist 
burning and a design which will tend to operate irrespective of the 
effects of excessive oiling and sooting. The Bosch Plug meets all 
these requirements. 

INSTALLATION OF MAGNETO 
Driving Method—Driving Speed. 

Since the magneto produces an ignition spark only at certain 
definite points in the rotation of its armature, it must be connected 
to the engine in such a manner that the spark is available always 
at the instant when required in the cylinder, i. e., about top dead 
center of the compression stroke. The magneto, therefore, must 
be positively driven from the engine by a method of drive that will 
eliminate slippage; belt or friction drive cannot be used. 

The Type DUG magneto, producing two sparks per revolution 
of its armature shaft, must be driven at one and one half times 
engine speed for six-cylinder, four-cycle engines, and at three 
times engine speed for six-cylinder, two-cycle engines. The type 
DU4 must be driven at engine speed (crank shaft speed) for four- 
cylinder, four-cycle engines, and at twice engine speed for four- 
cylinder, two-cycle engines. The type DUS must be operated at 
three-quarter engine speed for three-cylinder, four-cycle engines, 
and at one and one half times engine speed for three-cylinder, 
two-cycle engines. 

The type DU4-2, 360° is intended to be operated at engine 
speed on two-cylinder, four-cycle engines, the cylinders of which 
fire alternately every 360° revolution of the crank shaft; for 
two-cylinder, two-cycle engines, this type must be driven at twice 
engine speed. The type DU4-2, 180°, for two-cyhnder, four-cycle 




MAGNETOS AND IGNITION PRINCIPLES 


43 


engines, the cylinders of which fire at intervals of 180° and 
540°, must be operated at engine speed. 

The type DU2 must be driven at half engine speed (camshaft 
speed) for two-cylinder, four-cycle engines where the cylinders fire 
alternately every 360° revolution of the crank shaft; for two- 
cylinder, two-cycle engines, this type must be driven at engine 
speed. 

The type DUl must be driven at camshaft sped for single¬ 
cylinder, four-cycle engines,. and at engine speed for single¬ 
cylinder, two-cycle engines. Where the type DUl, two-spark, is 
used on two-cylinder, four-cycle engines, the Bosch Magneto 
Company, New York, or any of its branches, should be consulted 
as to proper driving speed. 

Direction of Rotation: The type DU magnetos are designed 
to run in one direction only, that is, clockwise or anticlockwise, as 
viewed from the shaft end of the magneto. The direction in which 
each magneto is designed to run is indicated by an arrow on the cil 
well cover at the shaft end of the magneto. 

TIMING THE MAGNETO 

With the average four or two-cylinder engine, the proper 
operating results are obtained by timing the magneto as follows: 

For types DU4-2, DUS, DUl, and DUG: The crank shaft is 
rotated to bring the piston of Number 1 cylinder (in automobile 
practice this is the cylinder nearest the radiator exactly on top 
dead center of the compression stroke, and the piston is to be main¬ 
tained in that position. The magneto is then to be secured to 
its bracket or bed on the engine, and the timing control arm on 
the interrupter housing placed in the fully retarded position. 

With that done, the magneto distributor plate should be re¬ 
moved by withdrawing the two holding screws, or depressing the 
two catch springs, as the case may be, thus exposing the distribu¬ 
tor gear and brush. The cover of the magneto interrupter hous¬ 
ing is also to be removed to permit observation of the interrupter. 

The armature should then be rotated by means of the exposed 
distributor gear in the direction in which it is to be driven until the 
platinum interrupter contacts are just about to separate, which 





44 


MAGNETOS AND IGNITION PRINCIPLES 


occurs when the interrupter lever begins to bear against one of 
the steel segments of the interrupter housing. 

The armature should be held in that position while the mag¬ 
neto drive is connected to the engine, due care being taken that 
the piston of Number 1 cylinder is still exactly on top dead center 
of the compresison stroke. The installation is completed by replac¬ 
ing the interrupter housing cover and distributor plate, and con¬ 
necting the cables between the magneto and spark plugs 

For Types DU2 and DUl: These, types should be timed to 
the engine in the same manner as described above for the types 
with gear driven distributor, except that with the DU2 and DUl, 
the dust cover over the armature should be removed to facilitate 
rotation of the armature by hand during the timing; the dust 
cover should be replaced as soon as the magneto has been connected 
to the engine. 

Exact Magneto Timing. The foregoing will establish the 
desired relationship between the magneto armature and the engine 
crank shaft. It should be noted, however, that while these in¬ 
structions cover the average engine, the exact magneto timing for 
individual engines is best determined by trial. Where specific in¬ 
structions for magneto timing are given by the engine manufactur¬ 
ers, it is recommended that such instructions be followed in 
preference to those herein given. 

HIGH TENSION CABLE CONNECTIONS 

For Types DU4-2, DUS, DU4, and DUB: After timing and con¬ 
necting the magneto to the engine in accordance with the foregoing 
instructions, and while the piston of Number 1 cylinder is still on 
top dead center of the compression stroke, it should be observed 
with which one of the metal distributor segments the distributor 
brush will be in contact when the distributor plate is returned to 
position, and the terminal stud attached to that distributor seg¬ 
ment is to be connected by a high tension cable to the spark plug 
of Number 1 Cylinder. 

The remaining distributor terminals should be connected to 
the spark plugs in the other cylinders according to the firing order 



MAGNETOS AND IGNITION PRINCIPLES 


45 


of the engine and the order in which the rotating distributor brush 
makes contact with the metal segments in the distributor plate. 
Thus the second distributor segment to receive contact is to be 
connected to the second firing cylinder, the third distributor seg¬ 
ment to receive contact is to be connected to the third firing 
cylinder, etc. In making these connections it should be borne in 
mind that the distributor brush rotates in the direction opposite 
to the rotation of the armature. 

For Type DU2: With the magneto interrupter and piston of 
the first firing cylinder in the position above described, the spark 
plug of that cylinder should be connected with the brush holder, 
the brush of which is in contact with the metal segment of the 
slipring, and this can be seen by removing one of the brush holders. 
If the metal segment of the slipring is not visible through the 
opening of the brush holder thus removed it is evidently in contact 
with the brush in the opposite holder, and the latter must in such 
case be connected to the spark plug of the first firing cylinder. The 
spark plug of cylinder Number 2 is then to be connected to the 
remaining brush holder. 

For Type DUl: With the type DUl, the installation is com¬ 
pleted by connecting a high tension cable from the brush holder 
terminal to the spark plug (or from both brush holder terminals 
to both spark plugs, in the two-spark type). 

BOSCH DUPLEX IGNITION SYSTEM 

The Bosch Duplex Ignition System offers a simple method for 
starting the engine at the slowest cranking speeds, by combining 
a battery circuit with any of the Bosch High Tension Magnetos 
arranged for Duplex Ignition. While this book deals only with 
“DU” types of Bosch Magneto, the same system has been applied 
to the “NU”; “ZU” and “ZR” types. 

Aside from the battery, the Bosch Duplex Ignition System con¬ 
sists of a duplex magneto and low tension duplex coil, the arrange¬ 
ment being such that, while the magneto circuit is complete in 
itself, as in Bosch independent magneto types, the battery circuit 
includes the battery and coil which act in conjunction with the 
magneto. The same set of spark plugs is employed for the mag¬ 
neto and battery both. 




46 


MAGNETOS AND IGNITION PRINCIPLES 


The battery side of the outfit is not intended to be used as a 
separate ignition system but merely as an auxiliary to the mag¬ 
neto to insure easy starting by cranking. 

OPERATION ON THE BATTERY SIDE 

Under this condition the primary winding of the magneto 
armature is included in the battery circuit, together with the 
duplex coil, and the action of the battery is to supplement the 
normal action of the magneto which, at extremely low speed, is 
not sufficient of itself to produce a high tension spark. 

As the magneto generates an alternating current which 
changes its direction of flow every 180 ° revolution of the armature, 
it is necessary, in order that the battery may assist the magneto, 
that the battery current be held in phase with'the magneto cur¬ 
rent, and for this purpose a commutator in simple form is pro¬ 
vided on the inner surface of the interrupter housing cover. By 
means of the commutator the battery current is caused to flow in 
the same direction as the magneto current, and a change in the 
direction of the latter is accompanied by a corresponding change in 
the direction of flow of the battery current through the primary 
winding of the magneto armature. 

With the starting of the engine, and at the slowest speed at 
which the engine will run, the necessity for the battery ceases, 
for at such a speed the magneto is capable of producing a satis¬ 
factory ignition spark. At this point there will be no difference in 
the operation of the engine whether the switch is left in the bat¬ 
tery position or is thrown to the magneto position. 

However, in order to reduce the battery consumption, it is ad¬ 
visable to throw the switch to the magneto position as soon as the 
engine has started. 

OPERATION ON THE MAGNETO SIDE 

When the switch is thrown to the magneto position, the bat¬ 
tery connection is interrupted and the operation of the magneto is 
identical in every way with the operation of an independent mag¬ 
neto. 

It should be noted particularly that the battery and duplex 
coil are employed in the battery circuit only, and not in the mag- 



MAGNETOS AND IGNITION PRINCIPLES 


47 


neto circuit, so that the removal of either, or both, would in no way 
affect operation of the magneto. 

BOSCH DUPLEX MAGNETO 

Aside from the interrupter and interrupter housing, which are 
described below, the construction of the duplex magneto is the 
same as that of the corresponding independent type, and complete 
information regarding the former may be obtained from the in¬ 
struction book for the latter. 

The interrupter housing cover consists of a fibre 
disc, which is maintained in a fixed relation to the 
housing by a key and keyway. The inner surface 
of the disc is provided with two metal segments, 
each connected to a terminal on the outer surface 
of the cover, as shown in the accompanying dia- Figure 14 
gram. The interrupter is provided with two brushes which, upon 
rotation of the magneto armature, sweep the two metal segments; 
the two segments constitute the commutator. This construction 




Figure 15 




48 


MAGNETOS AND IGNITION PRINCIPLES 


provides for the reversal of current necessary to hold the battery 
current in phase with that of the magneto. 

BOSCH DUPLEX COIL 

The duplex coil consists of a stationary cylindrical housing 
containing a simple primary coil, and the parts that form the 
switch. The housing is fitted with a flange by which it may be 
attached to the dashboard, bulkhead, or other support. 

The iron core of the coil carries a switch plate, embedded , in 
which are metal segments to which both ends of the coil winding 
are connected; by moving the switch handle, the segments in the 
switch plate may be brought into contact with contact springs on 
the stationary switch plate 9110, 9197 or 9501. The iron core also 
supports the coil cover 9186, which is provided with a switch 
handle by which the cover 9186, together with the coil winding 
and switch plate, may be moved as a unit from one switch position 
to another. 

The four coil terminals are connected electrically with the con¬ 
tact springs on the stationary switch plate, and are to be connected 
with the magneto and battery in accordance with the numbers and 
figures marked on the magneto and coil, and shown in the wiring 
diagrams on page 56. 

Press Button Style of Coil: The types “M” and “Ma” duplex 
coils, used in connection with several models of duplex magnetos, 
are provided with a press button which, under certain conditions, 
will permit starting on the spark. 

Where the press button is provided, it passes through an 
opening in the center of the core of the coil, and a spring causes it 
normally to project from the face of the coil. When the press 
button is depressed, its lower end comes into contact with an arm 
which, in turn, operates a make-and-break device carried on the 
inner side of the stationary switch plate 9110. 

The make-and-break device consists of a steel blade secured 
at one end to the stationary switch plate contact connected to coil 
terminal “Magneto 1”; the other end of the blade carries a supple¬ 
mentary blade with a platinum point. The movement of the make- 
and-break arm by the press button causes the platinum point on 
the blade to come into contact with, and then to separate from, a 



MAGNETOS AND IGNITION PRINCIPLES 


49 


second platinum point carried on the stationary switch plate con¬ 
tact connected to the terminal marked “Magneto 2/’ 

SWITCH 

The switch is in the “Off'' position when the cover is rotated 
in the left-hand direction to the limit of motion. 

The first position from that point is marked “Battery" and, 
with the connections then made, the system will operate on battery 
and on magneto. The ignition spark will then be produced by the 
action of the magneto current supplemented by that of the battery 
and coil. 

The second movement of the switch throws it to the “Mag¬ 
neto" position, and cuts out the battery. 

The stop screw 9076 limits in both directions, the movement 
of the switch. 

The switch is provided with a key lock, and this is so arranged 
that it may be locked and the key removed only in the “Off" 
position. This serves to protect the battery from being run down 
through the switch being left in the battery position with the 
engine at rest, and also prevents unauthorized operation of the 
engine. 


BATTERY 

The coil is wound for six volts, and a six-volt, sixty ampere 
hour storage battery is recommended. 

Dry cells may be used, however, in which case it is advisable 
to install ten, connected in multiple series. The cells should be 
divided into two groups of five, the cells of each group being con¬ 
nected in series, or, in other words, the carbon of one cell being 
connected to the zinc of the next. This will leave one carbon 
terminal and one zinc terminal of each group free, and the two 
groups should be connected by leading a wire from the carbon of 
one group to the carbon of the other, and a second wire from the 
zinc of one group to the zinc of the other. The arrangement 
described is shown on next page. 




50 


MAGNETOS AND IGNITION PRINCIPLES 


The wire from the carbon term¬ 
inal of the battery should then be 
led to the ‘‘Battery terminal on 
the coil, while the wire from the 
zinc terminal of the battery should 
be led to the “Battery—'' terminal 
on the coil. 

STARTING THE ENGINE 

By means of the Bosch Duplex System a spark sufficient for 
ignition purposes is produced at the lowest cranking speed, render¬ 
ing the cranking of any engine so equipped a comparatively easy 
matter. 

To start the engine, the spark lever should be fully retarded 
and the switch thrown to the battery position, the latter action 
placing the duplex coil, together with the battery, in series with 
the primary winding of the magneto. Under such a condition, at 
each separation of the magneto interrupter screws, the current 
from the battery passes through the primary winding of the mag¬ 
neto armature and induces in the secondary winding a current of 
very high voltage, which is more than sufficient for ignition pur¬ 
poses even at the lowest engine cranking speeds. 

When starting an engine equipped with the type “M’" or ”Ma” 
duplex coil, the spark lever should be fully retarded, the switch 
thrown to the battery position, and the push button on the coil 
depressed and released,. The arrangement is such that the bat¬ 
tery circuit is made and broken twice during the depression and 
twice during the release of the press button. It should be re- 
m.embered, however, that as the magneto interrupter screws and 
the press button contacts are in parallel, starting on the push 
button can be accomplished only when the magneto interrupter is 
open; pressing the button when the interrupter is closed will not 
break the primary circuit and under such conditions there will be 
no induction of high voltage current in the secondary winding of 
the magneto armature. 

If the engine does not start on the press button, it may be 
taken for granted that the cylinders do not contain gas, or that 






MAGNETOS AND IGNITION PRINCIPLES 


51 


the engine has stopped in such a position that the magneto inter¬ 
rupter screws are closed. It will then be necessary to crank the 
engine, in which case the action is exactly the same as with duplex 
coils having no press button. 

CURRENT CONSUMPTION 

As in the case with all battery systems, the current con¬ 
sumption will be highest if the switch is thrown to the battery 
position with the engine at rest. When the engine is started the 
current consumption drops immediately, but to preserve the bat¬ 
tery the switch should be thrown to the magneto position as soon 
as the engine starts. It will be noted that operation is positive 
with the switch either in the battery or in the magneto position. 
The necessity for the battery current to supplement the magneto 
current exists only at very low cranking speeds, and the assistance 
of the battery is unnecessary as soon as the engine starts. Inas¬ 
much as the battery and the magneto are connected in parallel, 
there will be no interference with the operation of the engine if 
the battery is disconnected, even with the switch in the battery 
position, as, under such conditions, the duplex magneto operates 
exactly the same as an independent instrument. 

CONNECTIONS 

The action of the system holds the battery current in phase 
with the magneto current, and it is therefore essential that the 
battery be correctly connected. If the connections are incorrectly 
made, so that the flow of magneto and battery currents are oppo¬ 
site in direction, no sparks will be produced. If the engine starts 
on pressing the button, or by cranking, but stops after it has made 
a few revolutions, it is safe to assume that the battery is wrongly 
connected. 

This fault may be corrected by reversing the battery con¬ 
nections either at the battery or at the coil. 

The reason for this action of the engine is that with the mag¬ 
neto at rest, there is no opposition to the flow of battery current, 
and it acts on the armature winding in a normal manner. With 
the starting of the engine and the rotation of the armature, how- 





52 


MAGNETOS AND IGNITION PRINCIPLES 


ever, the flow of magneto current is opposite in direction to the 
flow of battery current, and the inducing of high voltage in the 
secondary winding of the magneto armature is prevented. 

BATTERY SYSTEM MUST NOT BE GROUNDED 

The arrangement of the duplex system makes it imperative to 
prevent the battery current from becoming grounded, and ignition 
will cease in some or all of the cylinders if a ground connection 
occurs through a break in the insulation of the cables or from 
other cause. 

To guard against this, the insulation of the wires must be 
complete and the terminals properly protected. 

Dry cells are always provided with a pasteboard covering over 
the zinc element, and it must be borne in mind that if this paste¬ 
board covering becomes moistened, it will act as a conductor. If 
this condition exists in two adjacent cells, a short circuit will 
result. The most serious difficulty will be encountered when cells 
with moistened covers are used in a metal battery box. This will 
provide an absolute ground, and will render it impossible to run 
the engine on either the battery or on the magneto. 

The greatest care must be exercised to prevent the grounding 
of the battery. 

Furthermore, dry cells should be so arranged in the battery 
box that there will be no likelihood of their shifting from the 
vibration of the’ car or boat, in consequence of which the zinc 
terminals will come in contact either with each other or with the 
metal box. The best arrangement is to provide the box with com¬ 
partments into which the cells can be fitted. 



MAGNETOS AND IGNITION PRINCIPLES 


53 



INSTALLING THE DUPLEX SYSTEM 
The following points must be borne in mind in mounting the 
ignition system and in making the connections. 

1. The timing range of the duplex 
magneto, the speed at which 
they must be driven with rela¬ 
tion to the engine crank shaft, 
the manner of drive, also the 
procedure in connecting the 
high tension cables from the 
magneto to the spark plugs in 
the cylinders, are all exactly 
the same as with the corre- 
spending independent Bosch types. 

2. The battery connection and the connections between the bat¬ 
tery, coil and magneto, must be in strict accordance with the 
wiring diagrams. With the exception of the cables to the 
spark plugs, all connections are low tension and the wiring 
should be made accordingly. 

3. Great care must be taken to prevent the possibilty of the bat¬ 
tery becoming grounded, either through improperly protected 
terminals, faulty insulation, contact among the dry cells them¬ 
selves or contact between the dry cells and the metal battery 
box, due to moist or injured cell coverings. 

To avoid the possibility of trouble, all cables for connections 
to the magneto and coil should be provided with Bosch Loop 
Terminals, which will protect the cable against breakage and also 
prevent the straying of loose cable strands. Cables provided with 
large metallic terminals, or used without terminals, will usually 
lead to trouble through short-circuiting and breakage. 

Setting the Magneto: The magneto is to be secured to the 
base provided for it with the driving gear or coupling loose on the 
armature shaft. The engine should then be cranked until one of 
the pistons, preferably that of Number 1 cylinder, is at top dead 




54 


MAGNETOS AND IGNITION PRINCIPLES 


center of the compression stroke, and should be maintained thus 
until completion of the installation. 

The timing arm attached to the interrupter housing is to be 
placed in the full retard position, which is accomplished by moving 
it as far as possible in the direction in which the armature will 
be driven. 

The cover of the interrupter housing is to be removed to per¬ 
mit inspection of the interrupter, and the armature is to be rotated 
in the direction in which it will be driven, until it is seen that the 
magneto interrupter screws are in the act of separating. The 
armature is to be held firmly in that position while the driving 
gear or coupling is set tightly on the armature shaft. The cover 
of the interrupter housing is then to be returned to position and 
the setting is complete. 

The setting above described will render it possible to operate 
the engine, but the engine characteristics may make it possible 
that a slightly different setting will give somewhat better results. 
It is frequently the case that with the interrupter breaking in the 
full retard position when the crank shaft is about 5° over top dead 
center of the compression stroke, more satisfactory results will 
be obtained. 

The changes made in determining the best setting should be 
very slight, for a change of more than a few degrees rhay have'a 
marked effect on engine operation. Where specific instructions for 
magneto setting are given by the engine manufacturers, it is 
recommended that such instructions be followed in preference to 
those herein given. 

CARE AND MAINTENANCE 

Duplex Coil: The design and construction of the coil are such 
that there is very little which can possibly get out of order and, 
therefore, under ordinary conditions this unit requires practically 
no attention. 

If at any time the action of the ignition system becomes ir¬ 
regular, and it is suspected that the fault is in the coil, the coil 
body may be removed from the housing by withdrawing the hold¬ 
ing screw located at the “B’' position in the supporting flange; the 



MAGNETOS AND IGNITION PRINCIPLES 


55 


switch should then be unlocked and the coil cover given a quarter 
turn. This will release the cover, and the coil body may be with¬ 
drawn to permit inspection of the switch contacts both of the coil 
and the stationary switch plate. It may be that the spring contacts 
are ben or otherwise in bad condition. 

The withdrawing of the coil body should never be done unless 
it is certain that the fault is due to the coil; its handling under 
such conditions should be performed with extreme care. No work 
should be done on the coil in the way of withdrawing screws, etc., 
and il the inspection does not disclose the fault, the coil should 
be returned to its housing and the whole returned to the Bosch 
Magneto Company or its nearest official representative. 

Duplex Magneto: The instructions for care and maintenance 
of duplex magnetos, as well as for locating and remedying troubles, 
are tlie same as for the corresponding independent Bosch magneto 
types. 



56 


MAGNETOS AND IGNITION PRINCIPLES 


Wiring Diagrams for the Bosch Duplex Ignition System 




2. For Types “Lai” and Mai” Coils Figure 19. 








































































MAGNETOS AND IGNITION PRINCIPLES 


57 


DISTRIBUTOR PLATE 
WITH 

WATER PROOF CABLE FASTENINGS. 


INDICATOR POINT 
FOR SETTING MAGNETO 
TO MOTOR 



DISTRIBUTOR 

ROTATING 

DISC. 


SETTING 

^MARKS 


i CARBON BRUSH 
jfjO PICK UP 
CURRENT FROM 
COLLECTOR RING 


DISTRIBUTOR 
CARBON BRUSHES 


CABLE CONNECTION 
FOR COTTING off 
MAGNETO IGNITION 


MAGNETO CONTACT 
BREAKER POINTS 


WATER-PROOF END 
CAP FOR BREAKER 


TIMING LEVER BODY 


Figure 21. 


THE “G4-II EDITION” MAGNETO 


Since this booklet is intended as an instruction book, no gen> 
eral description will be attempted beyond a brief explanation of 
the fundamental differences between the 
Difference Between “G4-I Edit.” and the '‘G4-II Edit.,” to which 
I and II Edition latter this booklet applies. There are only 
two essential points of divergence, neither 
of which affects the interchangability of the magnetos on the 
motor. 

The flat spring style of contact breaker used in the I-Edit. is 






58 


MAGNETOS AND IGNITION PRINCIPLES 


replaced by a ‘‘rocker-arm’' type, of slightly more rugged construc¬ 
tion, in which the arm is actuated by riding over two flat steel 
cams, as can be seen in figure 21. 

The other chief difference is 
in the design of the frame, or 
housing, which is of a new 
unit-cast construction, where¬ 
as the I-Edit. housing was 
built up of several parts 
screwed together. This unit¬ 
casting has the advantage 
that it is extremely rigid, thus 
positively eliminating all 
danger of loosened screws or 
end plates, etc., due to vibra¬ 
tion or accidental twisting. 

Another benefit resulting 
from the absence of any joints 
is that it forms an absolutely 
water, oil, and dust tight pro¬ 
tection for the vital elements, such as the winding and the con¬ 
denser. Further, since it can now be bored out and machined all in 
one piece, and because of its rigidity, it is possible to hold more 
closely the running clearance between the armature and the poles 
of the magnets. This tends to give increased magnetic efficiency 
and, as a result, a much hotter spark. 

INSTALLATION 

Magnetos are made to turn in either direction, and care must 
be taken when ordering to state the correct rotation as seen from 
the driving end of the magneto. If no definite information is 
given about the direction, it will be taken for granted that it is 
required clockwise, and the apparatus corresponding will be sent. 
The direction of rotation is marked with an arrow on the driving 
end. The drive must be positive, either by gears or chain. We 
decidedly recomniend the use of the former in conjunction with a 
flexible coupling. 



Figure 22. 









MAGNETOS AND IGNITION PRINCIPLES 


59 


As two sparks occur in each revolution of the armature, the 
magneto must rotate as follows: 

FOUR-CYCLE MOTORS. 4 cylinders— 

engine speed. 

FOUR-CYCLE MOTORS. 8 cylinders— 

twice engine speed. 

As the spark occurs when the primary circuit is broken by the 
opening of the platinum contacts on the breaker mechanism, it is 
necessary that the magneto will be so timed 
Timing the Magneto that at full retard position of the timing 
to the Motor— lever body the platinum contacts just begin 

For Variable Spark to open when the respective piston of the 
motor has reached its highest point on the 
compression stroke. Turn motor by hand until piston of Number 1 
cylinder is on dead center (firing point), remove the distributor 
plate from the magneto and turn the driving shaft until the setting 
mark on the distributor disc is in line with the setting screw as 
shown in figure 21. (For magneto rotating clockwise, use setting 
mark “R”, and for anti-clockwise, use mark “L”.) With the 
armature in this position, the platinum contacts are just opening, 
and the metal insert of the distributor disc is in connection with 
carbon for number 1 cylinder. The driving medium must now be 
fixed to the armature shaft without disturbing the position of the 
latter, and the cables connected to the spark plugs. 

In fixed ignition where the timing of the spark never varies, 
the object in view is to find a medium between the occurrence of 
the spark at full retard and full advance. 
Timing the Magneto It must not occur too late, as the motor 
to the Motor— will overheat and lose power, nor occur too 

For Fixed Spark early ,as the motor will kick back when 

cranking, or knock when laboring hard, 
such as hill climbing, etc. It is evident, therefore, that the spark 
must occur before the piston reaches dead center, and as some 
motors, for certain reasons, can stand more advance than others, 
there is no predetermined rule for the timing which would apply to 
all motors. It is, therefore, advisable to find out from the maker 




MAGNETOS AND IGNITION PRINCIPLES 


of the motor at what distance before the piston reaches dead center 
the spark should occur for fixed ignition. 

With piston in position as mentioned above, the setting mark 
on the distributor should then be brought in line with the setting 
screw, and the driving medium (either coupling or gear) should be 
fixed in this position. 


MAINTENANCE 


It is impossible to place too much importance on the judicious 
oiling of the magneto. Hence, remember that the following in¬ 
structions are of vital importance.to the efficiency of the instru¬ 
ment in general and to the life of the contact points in particular. 

For lubricating the ball bearing at the breaker end, two oil 
wells with hinged covers are provided, one on each side of the 
housing, just back of the timing arm. Both of these lead 
Oiling to the same bearing and only the one which is most ac¬ 
cessible should be used. This well should positively not 
receive more than one drop every 1,000 miles or so. 

At the driving end two oil holes will be found. The larger one 
leads to the plain bearing carrying the distributor shaft and should 
be given about 15 drops every 1,000 miles. The smaller hole leads 
to the ball bearing at the driving end and should receive 4 or 5 
drops in the same distance. 

Good clean cylinder oil will do, but do not over-oil if you wish 
to avoid trouble. 

The contact points of the breaker mechanism and, in fact, the 
entire breaker itself, should be thoroughly cleaned with gasoline as 
often as they accumulate even a trace of oil or dirt. 
Cleaning The distributor rotating disc, the carbon brushes, and 
the collector ring should likewise be cleaned occasion¬ 
ally with a soft cloth moistened with gasoline. For obvious reasons 
all the parts should be allowed to dry before attempting to run. 

In order to obtain the best results the cables should be at 
once replaced if they show signs of cracking or wearing. 
Contact Points contact points should be inspected occasion¬ 
ally to see that they are clean and flat, and also 
that the maximum gap between the points is according to the 


Cables 





MAGNETOS AND IGNITION PRINCIPLES 


61 


gB,uge on the special adjusting wrench, or about 0.012" to 0.014." 

After a year of normal service it is advisable to carry in re¬ 
serve a few carbon brushes for the distributor plate, as well as 
an extra set of contact points. 

LOCATING TROUBLES AND REMEDYING THEM 

If the motor misfires or refuses to start, and the ignition is 
suspected, it should be found out first whether the trouble lies in 
the magneto or in the spark plugs. The latter should be examined 
first, as they are the most frequent cause of trouble. 

If the missing is in one cylinder only or in different cylinders, 
the corresponding spark plugs should be examined to see that the 
gap is not too large. This gap between the 
Spark Plugs electrodes should be between one sixty-fourth and 
one thirty-secondth of an inch. In no case should 
it exceed one thirty-secondth of an inch. On the other hand, a 
gap less than one sixty-fourth of an inch is liable to cause missing 
at low throttle opening. Also, the spark plug may be short- 
circuited through carbon or oil, or the insulation may be cracked. 
Cleaning with gasoline or replacing is the remedy. 

Clean same with gasoline until the contact surface appears 
quite white, or, if pitted, use a fine file—but very carefully—so 
that the surfaces remain square to each other. 
Burned or Pitted For this purpose a special file may be procured 
Contact Points from us at nominal cost. The correct gap of 
the contact points is 12/1000 (.3 m/m). 

As these contacts wear away in time, they should be regulated by 
giving the adjustable screw a forward turn, care being taken to 
securely tighten the lock nut. This can be accomplished, without 
removing the timing lever or breaker mechanism, by means of the 
combination wrench which is furnished with each magneto and 
which includes a gauge for the regulation of the gap between the 
contacts. It is very essential that this gauge be used, as the gap 
is very deceptive when judged by eye alone. 

If the contact riveted to the rocker-arm, or that of the adjust¬ 
able screw should be worn down entirely, it would necessitate a 




62 


MAGNETOS AND IGNITION PRINCIPLES 


change of either or both. When the adjustable screw is replaced 
or adjusted, care must be taken that the lock nut is securely 
tightened in place. 

Wiring The wiring should be carefully examined and checked in 
accordance with the firing order of the motor. If cables 
are cracked or chafed, they should be replaced. All connections 
must be kept clean and tight. 

If, after following these instructions, the motor still refuses to 
start, the magneto should then be tested by removing the dis¬ 
tributor plate and resting a screw-driver on 
Testing Magneto the gear casing, holding same about %" from 
the collector ring. Then, if upon rotating the 
armature, a spark jumps across the gap, it shows that the 
trouble does not lie in the magneto, but in some other part of the 
motor, possibly the carburetor. 

A re-magnetization of the magnets will only be necessary if 
these have been taken away from the apparatus and allowed to re¬ 
main a long time without both ends of the magnets 
Magnets being connected with a piece of soft iron. The same 
thing occurs if the armature is taken out of the pole 
pieces without a conducting rod of iron being laid across both 
poles. This piece must remain on the poles until the armature is 
again placed between the pole pieces. Often the magnets, after 
being taken down, are put back with one reversed and in this way 
the magnetic power is neutralized. To prevent this mistake, all 
our magnets are now marked, the north pole being designated by 
the letter ''N'' stamped in the magnet. W^hen replacing magnets, 
care should be taken to place the same poles on the same side. 





MAGNETOS AND IGNITION PRINCIPLES 


63 


EISEMANN HIGH TENSION DUAL SYSTEM 


The primary purpose of this system is to give two sources of 
ignition, magneto and battery, using one distributor and one set of 
spark piugs. The arrangement consists essentially of a direct high- 


DISTRIBUTOR PLATE 
WITH 

Oter^proof cable fastenings} 


INDICATOR POINT 
FOR.SETTING MAGNETO 
TO MOTOR 



DISTRIBUTOR 

ROTATING 

DISC. 


SETTING 

'MARKS 


^carboiTbrusiiv 

TO PICK UP CURREHTl 
FROM COUECTOR RINlg 


DISTRIBUTOR V 
CARBPH_.BRUSHES 


CABLE CONNECTION 

FOR CUTTING OFF MAGNETO. 

^ ignition; 


binding post 

FOR BATTERY 
BREAKER ' 


BATTERY CONTACT 
BREAKER POINTS 


TIMING LEVER BODY 


WATER-PROOF HUT 
FOR BATTERY 
CiNDING POST 


MAGNETO CONTACT 
BREAKER POINTS 


WATER-PROOF END 
CAP FOR BREAKCr.S 


Figure 23. 

tension magneto, used in conjunction with a combined transformer 
coil and switch which can be mounted on the dash. This trans¬ 
former coil is used only in connection with the battery, whereas 
the switch is used in common with both the battery and the 
magneto. 










64 MAGNETOS AND IGNITION PRINCIPLES 


The FJisemann Type “GR4'' magneto, as seen from the above 
illustration of its principal parts, is practically the same as the 
popular “G4” independent instrument with two main exceptions,— 
the timing arm is equipped with an extra, separate contact breaker 


Figure 24. Type “DC” Coil 


Figure 25. Type “DCR” Coil 


Figure 26. 




MAGNETOS AND IGNITION PRINCIPLES 


65 


for the battery current and the distributor is modified to permit 
of its electrical separation from the magneto armature when 
distributing the battery spark. 

This magneto may be used with equally good results with 
either of the styles of Eisemann dash coils, Type “D. C.'' (figure 
24) or Type ‘‘D. C. R.'' (figure 25). They differ only in the arrang- 
ment for starting ‘‘on the spark’’—the “D. C..” having a push but¬ 
ton giving a single spark, provided the motor happens to stand 
with the battery breaker open, whereas the “D. C. R.” has a 
mechanical ratchet device (see figure 25) delivering a shower of 
sparks regardless of the crank position of the motor. 

Rapid twisting, back and forth, of the starting handle on the 
front of ihe coil causes the toothed ratchet in the center, by acting 
against the fiber roller “A,” to oscillate the level “B”, which, in 
turn, makes contact alternately at “C” and “D,” giving a rapid 
sequence of sparks at the plugs. 

It might not be amiss to say a few words explaining the 
fundamental differences between the “GR4-I Edition” and the 
“GR4-II Edition,” to which this booklet applies. There are only 
tvo essential points of difference. 

The flat spring style of breaker used in the I-Edition is re¬ 
placed by a rocker-ai*m type, in which the arm is actuated by 
riding over the two flat steel cams, as can be seen in figure 25, no 
change whatever being made in the battery breaker. 

The other chief difference is in the design of the main frame, 
or housing, which is of a new, unit-cast construction in the II- 
Edil ion, whereas the I-Edition was built up of several parts. This 
unit casting has, amongst other, the advantage of being extremely 
rigid, thus positively eliminating the former possibility of loosened 
screws or endplates, due to vibration or accidental twisting. An¬ 
other benefit resulting from the absence of any joints is that it 
makes an absolutely water, oil, and dust tight protection for the 
vital elements, such as the winding and the condenser. Further, 
since it can now be machined and bored out all in one piece, and 
because of its rigidity, it is now possible to hold more closely— 
and even reduce—the running clearance between the armature 
and the pole shoes of the magnets. This tends to give greatly in- 





66 


MAGNETOS AND IGNITION PRINCIPLES 


creased magnetic efficiency and, as a result, a much hotter spark. 

Commencing with the II-Edition, the will have the 

improved form of distributor plate in which, by glancing at figure 
23, will be seen that the connection screws for fastening the cables 
are completely exposed to view alongside the respective carbon 
brush holders. This accessible location, together with the use of a 
screw with a large head, makes it a relatively easy matter to 
handle the fastening of the cables. Incidentally, this improved 
form of plate can be used on the I-Edition also. 

INSTALLATION 

Eisemann Magnetos are produced to turn in either direction, 
clockwise or anti-clockwise, looking from the driven end. The 
direction of rotation is plainly indicated with an arrow 
Direction on the shaft end. The drive must be positive, either 
of Rotation by gears or by chains. We decidedly recommend the 
and Speed former in conjunction with a flexible coupling. As two 
sparks occur in each revolution of the armature, the 
magneto must rotate at engine speed, for four-cylinder, four-cycle 
motors. 

As tne spark occurs when the primary circuit is broken by the 
opening of the platinum contacts on the breaker mechanism, it is 
necessary that the magneto will be so timed that at 
Timing the full retard position of the timing lever body the 
Magneto platinum contacts just begin to open when the re- 
to the Motor pective piston of the motor has reached its highest 
point on the compression stroke. Turn motor by 
hand until piston of No. 1 cylinder is on dead center (firing point), 
remove the distributor plate from the magneto and turn the driv¬ 
ing shaft until the setting mark on the distributor disc is in line 
with the setting screw as shown in figure 23. (For magneto rotat¬ 
ing clockwise, use setting mark “R,” and for anti-clockwise use 
mark “L.’O With the armature in this position, the platinum 
contacts of the magneto breaker are just opening, and the metal 
insert of the distributor disc is in connection with carbon for 
Number 1 cylinder. The driving medium must now be fixed to the 




MAGNETOS AND IGNITION PRINCIPLES 


67 


armature shaft without disturbing the position of the latter, and 
the cables connected to the plugs (see also '‘Wiring”). 

It has been found advisable in practice to time the battery- 
spark slightly later than that of the magneto itself. For this 
reason the battery on the Eisemann dual type instruments is 
permanently arranged to open 10° later than the magneto breaker, 
although subject to the same degree of advance and retard. 


A// c<7b/es shou/ d be pushed in os far as poss/6/e. /fisa/so 
very c7</i'/sa6/e fo conso/idofe fhe sfranded ends yvith 3o/cfer. 


Low Tension Cable 



mzh 


END CAP, 


for 

Hi gh Tension Cable 
(Strip for V/e)- 

■ Ti ghten bindin g 
screws firm/y. ' 


S pring for carbon 
brush can be re— 

piaced more eas- 

y/ y if the brush be 
revo/ved between 

the fingers wh/Ve 
being inserted. 

Figure 27. 



D/STR/BUTOE PL A TE 


The attaching of the cables to the spark plugs must be made 
in accordance with the firing order of the motor. For connecting 
between coil and magneto, see figure 27. The proper 
Weiring fastening of the cables to the distributor plate and 
end cap is of very great importance, in order to pre¬ 
vent water or any other conductor making a short-circuit between 
the different connections. Figure 26 illustrates and explains how 
these cables should be attached. This internal method of attach- 












































Wiring Diagram Showing Connections between “GR4” Magneto 
and either “DC” or “DCR” Coil 

Figure 28. 


68 


MAGNETOS AND IGNITION PRINCIPLES 



r 





GROUND 

















































































































MAGNETOS AND IGNITION PRINCIPLES 


69 


ing the cables to the distributor plate is another of our exclusive 
features, and makes a water-tight and solid connection. 

Important—The connection screw with the round head used 
in the distributor plate must not be used for the end cup, as the 
large head will not clear the revolving breaker mechanism. 

MAINTENANCE 

It is imposible to place too much importance on the judicious 
oiling of the magneto. Hence, remember that the following in¬ 
structions are of vital importance to the efficiency of the instru¬ 
ment in general and to the life of the contact points in particular. 

For lubricating the ball-bearing at the breaker end, two oil 
wells with hinged covers are provided, one on each side of the 
housing, just back of the timing arm. Both of these lead 
Oiling to the same bearing and only the one which is most 
accessible should be used. This well should positively not 
receive more than one drop every 1000 miles or so. 

Under the hinged cover at the driving end two oil holes will 
be found. The larger one leads to the reservoir which feeds the 
plain bearing cany ing the distributor shaft and should be given 
about 15 drops every 1000 miles. The smaller hole leads to the 
ball bearing at the driving end and should receive 4 or 5 drops in 
the same distance. 

Good, clean cylinder oil will do for all the oil wells, but do not 
over-oil if you wish to avoid trouble. 

The contact points of both the magneto and battery breakers 
and, in fact, the entire breaker itself, should be thoroughly cleaned 
with gasoline as often as they accumulate even 
Cleaning a trace of oil or dirt. The distributor rotating disc, the 
carbon brushes and the collector ring should likewise be 
cleaned occasionally with a cloth moistened with gasoline. For 
obvious reasons all the parts should be allowed to dry before at¬ 
tempting to run. 

In order to obtain the best results, the cables should be at 
Cables once replaced if they show signs of cracking or undue 
wearing. 



70 


MAGNfJTOS AND GNITION PRINCIPLES 


The contacts should be inspected occasionally to see that 
they are clean and flat, and also that the maximum gap 
Points between the points is according to the gauge on the 
special adjusting wrench, or about 0.012" to 0.014". 

We recommend the use of storage batteries with our 
Batteries dual ignition and our coils are designed to operate on 
six volts. 

A list of spare parts and illustrations of same are shown on 
pages 10 to 14. After a year of normal service, it is 
Spare Parts advisable to carry in reserve a few carbon brushes 
for the distributor plate, as well as a contact breaker 
rocker-arm and an adjustable screw. 


LOCATING TROUBLES AND REMEDYING THEM 


• If the motor misfires or refuses to start, and the ignition is 
suspected, it should be found out first whether the trouble lies in 
the magneto, the coil, or in the spark plugs. The latter should be 
examined first, as they are the most frequent cause of trouble. 

If the missing is in one cylinder only or in different cylinders, 
the corresponding spark plugs should be examined to see that the 
gap is not too large. This gap between the electrodes 
Spark Plugs should be between one sixty-fourth and one thirty- 
secondth of an inch. In no case should it exceed one 
Ihirty-secondth of an inch. On the other hand, a gap less than o: e 
sixty-fourth of an inch is liable to* cause missing at low throttle 
opening. Also the spark plug may be short-circuited througli 
carbon or oil, or the insulation may be cracked. Cleaning with 
gasoline or replacing is the remedy. 

Wiring The wiring should be carefully examined and checked in 
accordance with the firing order of the motor. If cables 
are cracked or chafed, they should be replaced. All connections 
must be kept clean and tight. 

Clean same with gasoline until the contact surface appears 



MAGNETOS AND IGNITION PRINCIPLES 


71 


quite white, or if pitted use a fine file—but very carefully—so that 
the surfaces remain square to each other. For 
Contact Points; this purpose a special file may be procured from . 
Burned or Pitted us at nominal cost. The correct gap of the con¬ 
tact points is 12/1000" (.3 m/m) for- both 
magneto and battery breakers. As these contacts wear away in 
time, they should be regulated by giving the adjustable screw a 
forward turn, care being taken to securely tighten the lock nut. 
This can be accomplished, without removing the timing lever or 
breaker mechanism, by means of the combination wrench which is 
fui*nished with each magneto and which includes a gauge for the 
regulation of the gap between the contacts. It is very essential 
that this gauge be used as the gap is very deceptive when judged 
by the eye alone. 

If the contact riveted to the rocker-arm, or that of the adjust¬ 
able screw should be worn down entirely, it would necessitate a 
change of either or both. When the adjustable screw is replaced 
or adjusted, care must be taken that the lock nut is securely 
tightened in place. 

If after following these instructions the motor still refuses to 
stai't, the magneto should then be tested by removing the dis¬ 
tributor plate and resting a screw-driver on the 
Testing Magneto gear casing, holding same about from the 
collector ring. Then, if upon cranking the 
motor, a spark jumps across g’^p, it shows that the trouble 
does not lie in the magneto, but in some other part, possibly the 
coil or the carburetor. 

- If the cables have all been checked up according to the wiring 
diagram and firing order, and if the system still refuses to work, 
although the magneto itself proves to be all right from 
The Coil the previous test, the trouble may lie in the switch 
mechanism of the coil. The design and construction of 
the coil, however, is such that it rarely gives trouble. 



72 MAGNETOS AND IGNITION PRINCIPLES 

If, for the above reasons or any other, it is desired to run the 
motor without the coil, it may be accomplished as follows: Discon¬ 
nect all wires leading from magneto to coil. Con- 
Running nect together the cables marked and on 

Without Coil the distributor plate, thus making a direct path for 
the high-tension current from the collector ring to 
distributor. The instrument can then operate as an independent 
magneto. A wire may be brought up from the “Ma'' connection on 
the end cap, to the dash and simply touched to any grounded 
metallic part of the car when it is desired to stop the motor. 

PRINCIPLE OF THE DIXIE MAGNETO 

In all electric generating machines the current is produced by 
cutting lines of magnetic force by conductors. This may be ac¬ 
complished in various ways, but the first two laws of electricity are 
basic for all designs. They are as follows: 

(1) An electromotive force is produced when lines of magnetic 
fo)’- e are cut by conductors. The effect produced is the same 
whether a conductor is moved so as to cut the lines of magnetic 
force, or the lines of force are caused to cut a stationary conductor. 

(2) The electromotive force produced is proportional to the 
rate at which the magnetic lines are cut. 

relation of MAGNETO SPEED TO ENGINE SPEED 

The speed of the magneto is always spoken of in terms of 
engine speed and the engine speed is considered as a unit for sake 
of convenience. 

The magneto speed is found by dividing the number of sparks 
required by the engine per revolution by the number of sparks 
which tlie magneto will deliver per revolution of its drive shaft. 

DIXIE magnetos will deliver one, two, or four sparks per revo¬ 
lution of the drive shaft. 

The speed at which the magneto should be driven on 4 stroke 
cycle engines is found in the following Table: 





73 


MAGNETOS AND IGNITION PRINCIPLES 


SPEED TABLE 


Moad 

No. of Cylinders 

Degrees 

Advance 

Sparks per Rev. 
of Magneto 

Mag. Speed to 

Engine Speed 

M-1 

1 

23 

1 

1/2 

M-2 

2 

23 

2 

' 1/2 

MRI-2 

9 

Fixed 

2 

21/4 

44 

4 

40 

2 

. 1 

46 

4 

40 

2 

! 1 

441 

4 

40 

2 

1 1 

442 

i 2 

40 

1 

1 

462 

2 

40 

1 

1 

481 

4 

30 

2 

1 

63 

3 

40 

1 . 

11/2 

64 

' 6 

40 

2 i 

1V2 

68 

6 

30 

2 

11/2 

612 

6 

30 

2 I 

11/2 

83 

8 

30 

4 i 

1 

84 

8 

30 

4 

1 

85 

8 1 

30 

4 

1 

86 

8 

30 

4 

1 

88 

8 

30 

4 

1 

800 

8 1 

Fixed 

4 1 

1 

825 

8 

Fixed 

2 1 

2 

124 

12 

30 

4 

11/2 


RANGE OF SPARK ADVANCE 

The number of degrees of advance effective on an engine is 
dependent on the speed of the magneto. Magnetos which run at 
engine speed have the same degree of advance effective on the 
engine as on the magneto. The advance effective on magnetos 
operating at other than engine speed is as follows: 

For magnetos driven at times engine speed, the effective 
advance is 2-3 of the range of the magneto, and for magnetos 
di’iven at V 2 engine speed is 2 times that of the magneto. DIXIE 
magnetos are made with different ranges of advance, suitable for 
















74 


MAGNETOS AND IGNITION PRINCIPLES 


engines of various types. The variation of the spark timing is 
accomplished by a lever, located on either side, or with double 
leverS; one on each side. 

SAFETY SPARK GAP 

A safety spark gap is provided as a protection for the insula¬ 
tion of the winding and other parts in the secondary circuit. The 
voltage of the.secondary current is proportional to the resistance 
which it has to overcome. If the magneto should be operated with¬ 
out one or more of the distributor wires connected, the safety gap 
provides a path for the high-tension current. The width of the 
safety gap should be from 5-16 inch to % inch, depending upon 
thi‘ compression in the engine. In engines where high compression 
exists, the safety gap should be set to % inch. 

Under high compression, the sparks may fire across the safety 
gap instead of firing in the engine. Misfiring under such con¬ 
ditions can easily be remedied by opening the safety gap so that 
it will ofier a greater resistance to the secondary current than the 
spark plug gap, under compression. Sparks should not be per¬ 
mitted to discharge across the safety gap for any great length 
of time. 

When two independent magnetos with two sets of spark 
plugs are used and the high tension leads disconnected from one 
magneto it should be grounded so that the sparks will not dis¬ 
charge^ across the safety gap when the other magneto is in use. 

THE DIXIE UNIDIRECTIONAL MAGNETO 

This magneto has been developed for use on high compression 
engines. It is called the Unidirectional type because it produces 
sparks of only one polarity. The DIXIE principle has been re¬ 
tained, with a modification of some of the parts. It is manu¬ 
factured in the following models: 

For 4 cylinder engines For 6 cylinder engines 

Model 481 Model 68 

Model 612 

In the 8 and 12 cylinder magnetos a field structure, rotor and 



MAGNETOS AND IGNITION PRINCIPLES 


75 


cam are employed which produce four sparks per revolution of the 
magneto shaft, two of the sparks being of one polarity and two of 
the opposite polarity. In the Unidirectional type the same field 
structure and rotor are used with a cam of slightly different 
design, so that only two sparks are produced per revolution of mag¬ 
neto shaft, both being of the same polarity. 

OILING 

The bearings of the magneto are provided with oil cups. These 
cups should be filled twice wdth a good grade of light oil before 
running the magneto for the first time, and should be similarly 
oiled thereafter as follows: 

Automobiles, every 1,000 miles. 

Trucks, every 500 miles. 

'Aeroplanes, every 25 hours of operation. 

Tractors, motor boats, and stationary engines, four drops of 
light oil every 20 hours of actual operation in the oil cup which is 
located on the top of the magneto just back of the distributor, and 
tw'o drops of light oil every 20 hours of operation in the oil cup 
on the rear of the magneto. 

Every possible precaution should be taken to prevent oil from 
getting on the platinum points, which will cause the magneto to 
operate unsatisfactorily, resulting in flashing at the contact points 
when running, and misfiring of the engine. 

INSTRUCTIONS FOR INSTALLING 

, One of the pistons of the engine should be in the proper 
position for timing as given by the manufacturer of the engine. 

Before placing the magneto on its support, care should be 
taken to see that there are no burrs around the holes in the sup- 
poi’t. The magneto should be set level on the support which carries 
it, and line up properly wdth the gear or coupling by which it is 
driven. 

The driving shaft of the magneto should be rotated in the 
direction in which it will be driven until the distributor brush is 
in contact with the segment Number 1, of the distributor block. 


76 


MAGNETOS AND IGNITION PRINCIPLES 


The circuit breaker should be closely observed and when the 
platinum contacts are about to separate, the drive gear or coupling 
should be secured to the drive shaft of the magneto. Care should 
be taken not to alter the position of the magneto shaft when 
tightening the nut to secure the gear or coupling, after which the 
. magneto should be secured to its support. 

The screws securing the magneto to its support should be 
drawn up tight, without springing the support or straining the 
threads in the base of the magneto. 

Where two magnetos are used on the same engine, one of them 
should be adjusted so that the point of firing conforms to the 
setting as given by the manufacturer of the engine. The other 
magneto should then be synchronized with the first one so that 
both magnetos will produce sparks at the same instant. This 
should be performed by means of adjustable couplings and not by 
the adjustment of the contact points or by shifting the breaker 
base. 


SETTING THE DISTRIBUTOR 

The distributor member is located on the distributor gear, 
meshing with the teeth of the pinion or driver in such a way 
that the contacts of the interrupter separate when the distributing 
brush is entirely on the segment with which it makes contact, 
when the timing lever is in the full advance position. 

It should be remembered that the distributor rotates in the 
opposite direction to that of the magneto shaft. When the mag¬ 
neto has been secured to its support, remove the distributor to see 
which terminal of the block is making contact with the distributing 
brush in that position. Connect that terminal to the Number 1 
cylinder and connect the remaining terminals around the dis¬ 
tributor block in the direction of rotation of the distributor to the 
remaining cylinders of the engine in the proper sequence in which 
they should fire. The firing order of the magneto is stamped on 
the distributor block. 



MAGNETOS AND IGNITION PRINCIPLES 


77 


THE LATE TYPE BATTERY IGNITION SYSTEM. 

The late type battery ignition system consists principally of 
a storage battery, high tension induction coil, distributor, inter¬ 
rupter points, and an ignition switch. It also has a condenser, and 
usually a resistance unit which is placed on one of the primary 
terminals of the coil. See Figure 29. 

Tracing the current when the ignition switch is turned on, 
and the interrupter points are closed, the primary or battery cir¬ 
cuit is completed; and the current immediately starts flowing 
from the positive terminal + and goes across the switch through 
the winding which is wound around the soft iron core of the coil 
to the insulated interrupter point to the grounded interrupter, and 
returns through the ground, which is the frame of the car to the 
negative side of the battery, thus completing the primary circuit. 
This current magnetizes the soft iron core, and sets up a mag¬ 
netic field in the coil as indicated by the dotted lines. ' Now, this is 
all that the battery current ever does in any ignition system; and 
the instant the interrupter points are opened, the battery current 
stops flowing, and the magnetic field dies out very rapidly, which 
causes a current of electricity to flow in the secondary winding, 
which goes to the distributor and is distributed to the different 
spark plugs in the proper firing order. You will see in Figure 30 
that the revolving segment is in contact with the terminal that 
leads to number I spark plug, and after the current jumps the 
gap at the plug it returns through the ground of the engine to the 
grounded end of the secondary winding from whence it started. 
You will note that in this system the primary and secondary wind¬ 
ings are not in any way fastened together; and it is not necessary 
as the battery current never goes to the spark plugs on any sys¬ 
tem. All the battery current does is to magnetize the soft iron 
core of the coil. The secondary current originates or starts in the 
secondary winding, and the instant the interrupter points open, 
the magnetic field dies out which causes the electricity that was 
already in the wire, to start flowing, and as it starts from the 
secondary winding it will return back to the secondary winding. 

The resistance unit on the top of the coil generally consists 
of a porcelain spool, which has a small coil spring made of German 



A LATE TYPE SINGLE WIRE BATTERY SYSTEM 



i, 

< C 

< < t 
( 


Figure 29, 







































A LATE TYPE SINGLE WIRE BATTERY SYSTEM 



Figure 30. 






























80 


MAGNETOS AND IGNITION PRINCIPLES 


silver wire surrounding it; and is for the purpose of regulating the 
flow of the battery current, and to keep the coil from being burned 
out, in case the switch was left on for any length of time. This 
resistance unit sometimes burns out, and in such case it would be 
necessary to replace it with a new one, or a substitute made of 
some other kind of wire, in order to get the system to operate. 

The condenser can be grounded on one side, when one of the 
interrupter points is grounded, but where both of the interrupter 
points are insulated as they are in the 'Two wire system,’^ it would 
be necessary to run an insulated wire from the condenser to the 
interrupter points, or connect it to a wire that does lead to the 
point. Condenser action has previously been treated. Note the 
position of the distributor segment with reference to the inter¬ 
rupter points in Figures 29 and 30. 



MAGNETOS AND IGNITION PRINCIPLES 


81 


QUESTIONS AND ANSWERS 

Q—What is electricity? 

4—No one knows any more than it is a form of energy which 
exists in every thing. 

Q—Can it be insulated? 

A—Yes. 

Q—^Why do we insulate it? 

A—To make it go where we want it to go, and to keep it from 
going where we do not want it to go. 

Q—What sets electricity in motion? 

A- —In the case of a storage battery, it is the chemical action. But 
with the generator it is set in motion by the armature cutting 
lines of magnetic force. 

Q—^What is magnetism? 

A—Magnetism is a phenomenon of which there is very little 
known, and cannot be insulated. It can be created by winding 
an insulated wire around a soft iron or steel core, and then 
sending a current of electricity through the wire. 

Q—^What would happen if magnetism should cease to exist ? 

A—All of our dynamos would stop immediately. 

Q—^W^hat metals are good conductors of magnetism? 

A—Iron and steel. 

Q—^W^hat metals are called non magnetic ? 

A—Brass, copper, aluminum, zink, and carbon. 

Q—^What is the law of induction? 

A—Place a coil of wire in a magnetic field and cause the field to 
vary, and there will be a current induced in the wire, or by 
moving a coil of wire rapidly in a magnetic field will induce 
a current in the wire. 

Q—^What is an electro-magnet? 

A—A soft iron core wound with an insulated wire, and is only a 
magnet during the time that a current is passing through the 
wire. 

Q—^What governs the strength of a magnetic field? 

A—The strength of an electro-magnet is governed by the number 
of turns of wire, the strength of the current flowing, and the 



82 


MAGNETOS AND IGNITION PRINCIPLES 


quality of the path through which the lines of force have to 
travel. 

Q—How does a magneto generate a current? 

A—By cutting lines of magnetic force. 

Q—Can electricity be stored? 

A—No. It is the electro motive force that is stored and not the 
electricity. 

Q—^What is electro motive force? 

A—Electro-motive force is called the E M F or electrical energy, 
which is the same as voltage, or pressure. 

Q—Do all dynamos generate an alternating current ? 

A—Yes, but the ‘'so called'' direct current generator by the use of 
a commutator, transforms the alternating in to direct current, 
before it leaves the generator. 

Q—What is a permanent magnet ? 

A—A permanent magnet is a piece of hard steel which has been 
magnetized. 

Q—^W^hat is the meaning of A. C. and D. C. ? 

A—A. C. stands for alternating current and D. C. for direct 
current. 

Q—^Why is an A. C. generator better for ignition purposes than 
aD. a? 

A—Because of the raid building up and dying out of the core of 
the armature, which is caused by the reversal of polarity 
every 180° which is each half revolution of the armature. 

Q—^Why is the high tension magneto the most efficient and reliable 
for ignition purposes ? 

A—Because of its simplicity, and few wires, and the condenser is 
close to the points and the core where it will do the best work, 
and it will not freeze up, as will a battery, and it will also give 
a more volumnous spark. 

Q—How many windings on a low tension magneto? 

A—One heavy insulated, winding, called the primary. 

Q—^What is the voltage of a low tension magneto? 

A—From 6 to 30 volts depending on the speed at which it is driven. 



MAGNETOS AND IGNITION PRINCIPLES 


83 


Q—^Why does a low tension magneto need a high tension coil in 
connection with it ? 

A—To step up the voltage, and make it sufficiently strong to jump 
the air gap at the spark plugs. 

Q—^What is the voltage of an H. T. coil ? 

A—From 12,000 to 25,000. 

Q—^What are lines of force? 

A—They are invisible lines of magnetic force which flow from the 
north to the south pole of a magnet. 

Q—What are the magnets of a magneto for? 

A—To create a magnetic field. 

Q—Will a magneto produce a good spark if the magnets are weak? 

A—No. 

Q—What are the pole shoes made of, and what are they for? 

A—They are made of soft iron, and are for the purpose of filling 
the air gap between the magnets and the armature. 

Q—Why is the base of a magneto made of a non-magnetic ma¬ 
terial ? 

A—To keep the lines of force from going through the bottom of 
the magneto, and cause them to go through the armature. 

Q—^What are the three types of armature, used on magnetos ? 

A—Shuttle, inductor, and rotor. 

Q—^Why is it necessary to have the core of A. C. generator 
laminated ? 

A—To reduce eddy current, and give a greater surface to the flow 
of the lines of force. 

Q—^What is a luminated core ? 

A—A laminated core is made of sheets of soft iron, or sometimes 
a bundle of soft iron wire, insulated from each other with a 
special varnish. 

Q—What makes a magneto generate an alternating current ? 

A—^A magneto generates an alternating current, for the reason 
that the armature is constantly changing its position in the 
magnetic field. That is, the lines of force flow through the 
armature in a different direction every 180 degrees. 

Q—Of what does the primary winding consist? 

A—The primary winding consists of a few layers of coarse insu- 



84 


MAGNETOS AND IGNITION PRINCIPLES 


ated wire, and on a magneto, one end is grounded to the core 
of the armature. 

Q—Of what does the secondary winding consist? 

A—^The secondary winding consists of several thousand turns of 
very fine insulated wire; it is wound over the primary. 

Q—How many current impulses will a shuttle type armature pro¬ 
duce in one revolution? 

A—A magneto with a shuttle armature will not produce over two 
current impulses in one revolution. 

Q—How many current impulses will an inductor type armature 
produce in one revolution? 

A—^A magneto with an inductor armature can be made to pro¬ 
duce four current impulses to each revolution,- by using a four 
cornered cam, which will open the breaker points four times to 
each revolution. 

Q—What are the interrupter points for ? 

A—To make and break the primary circuit, which causes the mag¬ 
netic field to build up or die out at the time a spark is needed 
in the cylinder. 

Q—^What material are the interrupter points usually made of? 

A—Platinum or Tungsten. 

Q—^What is the proper adjustment of the interrupter points? 

A—From 12 to 17 thousandths on a high tension, and from 25 to 
30 thousandths on a low tension magneto. 

Q—How can the interrupter points be trued up? 

A—With a platinum file. 

Q—^What will happen if the points do not open the proper 
distance ? 

4—The motor will miss fire and may stop entirely. 

Q—^What is an indication of a poor condenser? 

A—An excessive amount of sparking at the interrupter points. 

Q—What is a condenser made of? 

A—Tinfoil and is insulated with paraffined paper or mica. 

Q—Where is a condenser located? 

A—It may be located any place in the ignition system, so long as 
it is connected across the interrupter points. 

Q—How can a condenser be tested ? 



MAGNETOS AND IGNITION PRINCIPLES ^ 85 

A—^With a 110 volt lighting system, either D. C. or A. C. 

Q—In what circuit is the condenser placed? 

A—It is always placed in the primary circuit. 

Q—^What is a distributor for? 

A—It is a revolvong switch, and its function is to distribute the 
H. T. current to the spark plugs in their proper firing order. 

Q—From which end of the magneto is the direction of rotation 
determined ? 

A—The driven end. 

Q—^What is meant by clockwise? 

A—To travel in a right hand rotation, the same as the hands of 
a clock. 

Q—^What is meant by anti-clockwise ? 

A—To travel in a left hand rotation, opposite to the hands of a 
clock. 

Q—^What is meant by advance and retard? 

A—To move the breaker box against the direction of rotation 
is advance, which causes the breaker points to open earlier. 
Retard is to move the breaker box with the direction of rota¬ 
tion, which causes the breaker points to open later. 

Q—^What is a high tension induction coil? 

A—A coil with a primary and secondary winding. 

Q—^What is the voltage of an H. T. coil? 

A—From 12,000 to 25,000. 

Q—^What is the voltage of a H. T. magneto? 

A—From 10,000 to 20,000, depending on the speed that it is 
driven. 

Q—How many windings has an H. T. magneto? 

A—Two—primary and secondary. 

Q—How is a H. T. magneto timed? 

A—The same as a low tension magneto. 

Q__What is meant by the magneto speeds? 

A—It means how fast will the armature have to travel, with 
reference to the end speed. 

Q—At what speed should a magneto with shuttle type armature 
be driven on a 4, 6, 8, and 12 cylinder engine ? 

A—Engine speed on a 4, once and a half times engine speed on 




86 


MAGNETOS AND IGNITION PRINCIPLES 


a 6, twice engine speed on an 8, and three times engine speed 
on a 12. 

Q—At what speed should a magneto with an inductor type arma¬ 
ture be driven ? 

A—It is usually governed by the same rule as that of the shuttle 
type, but the K. W. high tension magneto is so designed that 
it can be driven at engine speed on a 4, or by using a four 
cornered cam it will produce 4 current impulses to each revo¬ 
lution, and can be used on an 8 cylinder motor and still be 
driven at engine speed. 

Q—At what speed should a rotor type be driven? 

A—See Dixie Magneto, page 73. 

Other books on Electric Starters and Generators, covering the 
entire electrical equipment of the automobile now in course of 
preparation. For information write to Cedric S. Webster, Box 144, 
Independence, Missouri. 








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